i know there are some great engine builders here

[Adger Smith]

Well as an old time builder I have a totally different take on the bearing clearance/side clearance topic.
First I would like to point out that it appears like some didn't grasp what was going on with the side clearance. I think it was a product of misinformation. It was an intentional misdirection of information.
Back in the day we had to use to use wide clearances to keep bearings and engines alive. Oil flow was not the real issue. The real issue was flex and parts moving around rubbing, touching and binding.
1. The older crank and rod material was not as strong as we have today.
The alloys were different and today the stock parts are stronger by design, too.
2. The size made a difference in the strength. As SBC cranks went from 2" rods to 2.100 they flexed less and bearing clearances and side clearance could be closed up.
3. The weight of parts decreased so the loads on the crank and rods decreased.
Modern day pistons and pins are stronger and lighter.
As the parts got better the clearances could be decreased.
I did find that some engines with large diameter mains and rod journals needed more clearance just for the growth created by the heat. I used the unscientific method of heating parts to operating temps to find the running clearances. The first pin guided rod I ever saw was in the model airplane engines we used as kids. As I started racing go carts I saw them used in the chainsaw engines we modified. There is quite a difference in what we had back then vs what we have to work with now. Progress...
I think the engine Guru's of that time never discussed the real issue of parts flexing. That was a real speed secret.