Lot of things to update here but the short story is I finally have AC.
I tried to locate a fatter o-ring both online and at a couple auto parts stores with no luck. Thought I'd look through the bag of o-rings I ordered along with the parts (didn't realize they all would come with o-rings already) and didn't see any that looked fatter. As I was putting them away though I did notice a fatter one. I presume it was possibly one that was included with the condensor that got mixed in with the others. When I was preparing parts to install I just threw all the o-rings in with the package I had ordered, not thinking they might be specialized (other than the obvious different sizes). Here's a photo showing the difference. I have 20 or so of the narrow o-rings of this size but only one fat one. Why the manufacturer makes this fitting different is beyond me.
I re-installed the condensor and low-pressure hose (for the third time) and hooked up the vacuum again. It seemed to be working so got the truck up to operating temperature and left the vacuum running for an hour or so. When I went to disconnect the manifold gauge from the low pressure valve the low pressure valve was making a hissing noise as if it was leaking. I connected up the gauge again and checked pressure and it seemed to be ok, but when I disconnected it again the valve again hissed a little.
I had seen a video of a guy demonstrating an AC fill and he said that the schrader valves can get bent from the manifold gauge couplings. So I wondered if that's what happened. I happened to have a Schrader Valve replacement kit that the idiots at Autozone convinced me to buy, so I thought I would try to swap out the valve quick. Well, it was the wrong size. Yes, even though I asked if all Schrader valves for ACs are the same at Autozone and the manager assured me they were (without checking) they are in fact different sizes. So I put the original back in and tightened it up, hoping maybe it had just worked loose.
Pulled a vacuum again for a bit. Then decided to deal with this problem I had of attaching the new-style r134a cans (with a self-sealing valve rather than puncture-type). The geniuses at Autozone sold me an adapter to fit the cans for use with a puncture-style filler. I have an old puncture-style filler/gauge, but obviously it would be better to fill through the yellow hose on the manifold gauge set. Of course, Autozone doesn't sell the correct adapter. Advance Auto does, but when I drove to the nearest store after checking online and seeing it "in stock" they didn't have it in stock. The next nearest store had one so I called from my truck to see if they actually had one. I gave her the part number and she told me I just called asking about it. What? Then she asked me if my name was "Don." No, my name isn't Don and I didn't just call. Do you have one or not? haha. She said someone else had just called asking about that adapter and had asked her to hold the only one they have in stock for them. haha. So I drove home and check stock everywhere online. The only place showing inventory is all the way across town, an hour-and-a-half roundtrip. I call to make sure they have it, they do (he's holding it in his hand), so I set off across town.
Meanwhile, I yesterday finished replacing the drums, shoes and hardware in both my rear wheels. I had to order a Rear Parking Brake cable as the one that was in there was the wrong size (for heavy-duty suspension maybe?). Anyway, so those drums were a TIGHT FIT, even with the spreader dialed all the way down. I was pretty sure they were in decent shape for driving, but wasn't sure I wanted to be driving at Interstate speeds for an hour because I wasn't sure how much heat might build up. Anyway, they weren't making noise or anything, just a little tiny bit of drag. So I drove on regular streets all the way over there. Oh, and it was 93-degrees here today and of course it was humid. At least I have the new stereo in my truck so I didn't have to listen to the wind blowing through the open windows.
Got the part, drove home, checked the vacuum, still holding, pulled vacuum again for another half hour or so, hooked up the can to the adapter, weighed it, let a little r134a into both sides with engine off (a very little- no waiting for both sides to equalize or whatever that means from the original op), started the truck and began filling. The compressor didn't kick on for a bit even though the low pressure was running pretty high. After 16-oz. or so was added the compressor began running. I was pretty excited about this as if you read the original post I had wondered if I destroyed my new AC system. So everything went good pretty much from there. I used a kitchen scale to weigh out how much refrigerant I was putting in (spec for my 1998 is 30oz.) and lucked out to get it right at 30.00 oz. Cold air blowing thorough the vents. Pressures looked pretty good; they mostly sat at these levels after bouncing around earlier in the process. The one concern I had was that the thermometer I used at the vent was only showing about 60-degrees, but this was possibly due to the crappy thermometer I used or the fact that sun was shining on it too.
Checked just a little while ago and AC is still working good. Working so good I could only leave the blower on level 1 as it was getting too cold even though it's still near 80-degrees and humid outside. So now it's just a question of if it will continue to hold pressure. I'm a little reluctant to check as I did have those problems with that valve, so I might just see how it holds up for a bit. Thanks again to those who offered some help. Unfortunately this was the type of project and I had the sort of problems that I mostly just had to muddle through and figure out on my own.