the d60 killed my 308 dreams.....308 with 33s makes for good cruise speed with a turbo.
i run 410 gears and 37 in military, and they are ok with the non turbo application on the road, but seriously cut into economy.
with 33 in tires and 50-55 mph 20 mpg was easy with nearly 26 on a few trips when this engine was in the young 200 k range, but my injectors are totally trashed now and i get 15-17 with the 37's at 55-65. town is pretty much the same now too
...its well over 300 k working to 400 now so its days are numbered.
see what happens with fresher engine and injectors. i suspect a good 4bt in my same situation would pull 23-25 easily.....likely 17-19 town. but would be slower to get to speed unless cranked up.
i am working with some different transmission mount applications currently. i have a different idea i want to build and try. this setup used for engine and trans with a 4bt may be a good way to go.
i found the 4bt too loud and vibration prone to fit my taste. but it certainly is more economical to operate.
with the manual trans i am confident you will be satisfied with the fruits of this work even as involved as it is....