Shop manuals say # 1 upper is not interchangeable with 2-4-5. Is that still true or all clevite upper bearing chamfered. I cant see a difference in them

In the old days the number 1 upper had a slight chamfer on the parting line to direct oil at the chain. I believe that stopped many years ago. You can do the same thing if you want - a few slight passes with a file gets you the same end result.

That was on the OEM bearings and some of the after market manufacturers did that for a short while in the mid 1960s
I don't see any bad results on chain life without that little chamfer

Agreed Cab, I think it was early on and powertain engineering always seemed to be extra cautious back then.

If you think about it the #1 cam bearing pressurized lube leaks out the back and front of the bearing. What leaks out front lubes not only the cam sprocket to block thrust face (which is loaded rearward) but also lubes the chain and sprocket teeth by centrifugal force.

Look at all the changes the small block went through for the same lube concerns - cam thrust plate lower bolt with hole, drain tab, etc.

If I recall all that went away too in later years, relying on lube from #1 cam bearing to lube the thrust plate, sprocket and chain.

I drilled a 3/8 hole in the SB flat cam plate then drilled/tapped the front of the pass horizontle oil gallery for a blue alum pipe plug & drilled a .015" hole in it for a constant squirt out onto the chain.