Your way better off building a 400 block based stroker motor for the increase strength in the main webs for either size C.I. I've seen 4 or more RB blocks with cracked main webbing from drag racing them, no 400 blocks yet I have never heard of a 400 block cracking the main webbing from making to much HP either They will crack the main caps if you use the stock main caps and stock main bolts on a race motor and detonate the motor, no troubles if you use after market main cap and main studs
I built a 440 based bracket race motor with the 4.375 stroke with a 4.375 bore years ago before I became aware of the main webbing problems I used it as a dyno mule and tested a bunch of different heads, intake and carbs. It made 845 HP that last time I had it on a DTS engine dyno with a set of CNC ported 440-1 heads with a 440-3 intake and a Holley #9375 non HP Dominator carb using the local 110 octane race gas
The same size C.I. 400 block stroker motor with all the same parts will make the same power and probably last a long time longer when racing it compared to a 400 block build