how much horsepower a 351m/400 block can handle
 

i was thinking if i turbo this engine what would be the hp limit before the stock rods break and the block cracks and wut about the crank if i was going to do this work i would do a rebuild with Arp bolts and copper head gaskets

With a stock engine just turbo charged, something would go wrong. If you did a complete rebuild and turboed it, it should hold up fine.

Assuming a good rebuild with quality parts including forged pistons and a reasonable boost pressure you should be able to easily run up to 500 HP as long as you put some sort of rev limiter in it to keep under 6000 RPM. I would definitely make sure to keep the static C.R. around 7.5:1 to avoid detonation issues. 351M/400 heads aren't known for their great resistance to pinging/detonation.

I think ShaZam had around 700 horses with his... I think thats his username.

Mine makes around 385... no problems with it.

i think 650 is about the limit. just have the block checked ofr cracks and make sure to have the engine balanced.

ShaZam did some other mods to his pulling 400 like putting filler in the block that you probably wouldn't want to do with a street engine.

i think it was 799/863 and about 16,000usd
and streetable if the lights are what 1/4 mile away and a long cooldown wait bween lights sounds fun but not real effective

but anyway isn't the wall thinnest at the bottom and furthur could you fill an inch or two up providing you can keep it 'level'