How do I fix this??

[Brian]

Thanks,
Gary; to try and answer your questions; There is a definite pattern, inasmuch as all conrods are closer to the rear of the piston boss. The worst one is as pictured, cyl's 1 & 5, where the clearance is 0.020" at the back. How much is the least amount of clearance I could get away with? I could ,as you suggest, grind a bit off of the small end, but, Geeze, I shouldn't have to!
I think I can get away with all the other cylinders; minimum clearance on the rest would be 0.080".
Lonnie,: this is definitely a crank issue.
Incidentally, the pistons I ordered as specials from Ross, 4" stroke 3 3/16" bore flat tops. Same as 49-53 Merc but with flat tops not domed. It wasn't until I went to do the initial mock up, that I realised they hadn't machined inside the gudgeon bosses, and the conrods wouldn't fit. I was at work until midnight last night machining the required clearances. I notified them of their oversight, they said 'sorry'. At least that is a [ever so slightly] better response than I got from Scat when I told them about the main bearing issue. I need to follow Tony's suggestion from that earlier thread, I am over building these old things!! Too much agro, things were so much easier when I was young and knew nothing!!