I'm rebuilding a 1973 B-20 4 cylinder push rod Volvo motor that was bored .030 over. Tough as nails old "tractor" motor- no overhead cam shafts or timing belts or aluminum heads to corrode- just good old cast iron.

I just got the block back from the machine shop with new cam bearings and hot tanked. Rods were checked and didn't need new wrist pin bushings
everything is looking good.

so today I cleaned all the engine parts---installed the pistons on the rods
and started checking the pistons/rings
Deves rings
after reading the installation sheet that came with the rings
I was measuring the fit of the top ring in the piston and I could not get .006 to fit between the ring and ring groove so that piston was still good .

Then I noticed that the ring is the same size as the top of the piston seems to me that the ring should be bigger diameter
It was too late to call the parts place tonight-
my piston tops are 89.5mm(little more than 3 1/2") and the rings are 90mm
there is almost a 1/2" gap on the rings uninstalled

I'm pretty sure that they sent us the wrong piston rings-

anybody know the correct ring gap for that size of piston 89.5mm or 3 1/2"
I'm sort of remembering that it is .004 for each inch of piston does that sound about right
.004 x 3.5= .014 ring gap

How can I figure what size rings to order I've already told the parts place the piston size and maybe they just messed up and sent the wrong ring

spiritual advice welcomed
thanks
hank