I have a 400 block with stock forged crank and rods from a 383 and i will be getting forged pistons (9 to 1 comp) Stealth alm heads. will it survive if i put on a paxton certifical SC on it with 5-6 boost? i would like to upgrade later with a new pulley to get 6-8 psi later. just want to make sure the stock parts will make a solid bottom end. thanks

It should be fine. I run a stock bottom end on the TT440. It's got the cheapie Speed Pro forged pistons from Summit. The bottom end survived way too much detonation while I was learning to tune it with 8 psi. I ran 15 to 17 psi for a while and even surged it to 22 psi by accident.
The detonation transferred metal from the piston crowns to the cylinder walls and blew the head gasket. There has never been a problem with the rods and crank. The bearings weren't hurt too bad either.

You would be fine without forged pistons. I had a 100% stock bottom end 383 I ran 13-15 psi on for 3 years. I learned how to tune on it. I even forgot the hook up the timing retard after setting the timing and ran it on 15 psi and 35* timing. The head gaskets didn't really like that but the motor lived fine.

I never had a problem with my stock 383 crank, rods, rod bolts, or pistons with 8psi.

just my boost referenced Holley mechanic pump

Thanks all for the reply, If i cant manage to land some .040 forged pistons I will just stick with the cast ones. I planned on using the paxton NOVI 1500 kit from shophemi.com and using boost ref MSD timing and fuel reg. upgrade pulley and to a intercooler later.