I hope you are not planning to run that speed continuously.
To the best of my knowledge the biggest you can go for big bore is
2200cc which is about 3 11/16". B21 bore is 3.622" Standard B21
pistons will only work in an 8-bolt engine. IPD used to sell pistons
for 6-bolt engines but I don't know if they do now or not. If not,
there are Chevrolet pistons that can be made to work (removing the
small end bush and honing a bit) that start at 3.570 and can be gotten
in oversizes up to 0.060", which gives you a bore of 3.630, same ballpark.

The main structural thing that limits rpm (NOT Torque!) is piston weight
and as far as I know the pistons weigh about the same.

You need to have your block bored by an experienced machinist because
there is a possibility of a cylinder being cast slightly eccentric and
thus the boring bar needs to be moved laterally so that the bore corresponds
to the water jacket. As the cylinder becomes thinner with bigger bores,
this becomes a lot more critical. The one big bore I had ran great and was
for 10 years the best engine I ever built. But when I ran a 5/16" hex nut
through #2 cylinder, the BLOCK was destroyed, without substantial damage to
either the piston or the head. The nut got between the flat portion of the
head and the piston, cocking the piston in the cylinder, and splitting the
cylinder from the bottom to the top, an opening you could stick a spoon
handle through. The block appeared to be about 3/32" thick where it split.
That was a 0.122" overbore or only 0.061" removed from each side. In my
opinion, even 0.150" (the original thickness) is marginal for a good stable
cylinder. Looking back, I'm surprised it ran as well and as long as it did!
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma