FWIW, synthetic has, generally, a lower viscosity than natural based oils. 0W20 is pretty thin, hot or cold. Given that, I would think the long chain polymers that uncoil like a spring when heated, and increase effective viscosity, are used more heavily in synthetic.
Start-up tapping of the lifters is generally due to leak-down of the lifter in question. It does not make much difference in engine life. There is a leaky check valve or some 'dirt' making the valve leak. The valve spring pressure is constant, and trying to 'leak down' the lifter overnight, or any time the engine is still. If you have decent oil pressure, the tapping should go away within a few seconds, and cause no harm.
I think the lower viscosity of the synthetic will often lead to seepage past seals that formerly were seeping so little it was 'invisible'. You just didn't see the seepage, it was so small.
If your engine does not run excessively hot, then you are paying for synthetic protection from heat breakdown that will not be used. Synthetic was developed to be used in gas turbine engines immediately after WWII. The heat in a turbine broke down natural oils, and they turned to brown/black gunk. They were burning instead of lubricating and carrying off bearing heat. Not good. So syns were developed to solve that problem. You don't have that problem in a Lima, even at the worst case.
If you do the math, using synthetic oils won't pay for itself in increased oil change intervals nor in extended engine life. Most Limas can go 300k without whining, using natural based oils. Synthetic may extend that, due to slightly quicker flow when cold, but the extra cost per quart will likely not pay off for the average user.
So, to sum, you get extended intervals before a change is required, but how long? I dunno. You also get the likelihood of seepage increased, not all, but some. So you will likely leak some synthetic. You may get a bit better flow when cold, but if you used a 5W20 synthetic blend, as spec'd for some Ford engines, you'd get the quick flow of a 5W and the protection from heat of a synthetic.
You pays your money, and you takes your chance. Winna winna chicken dinna ... or not. Your dollars, your engine.
My lima was not spec'd for 5Wanything, but 10W30 as its 'natural' oil diet. I may put some synthetic in to perhaps keep the can lobes from grinding away, but I don't know if it will really help. No more ZDDP may eat the cam. We'll see.
tom