what is a dash 8 block and what is so special about it and second will it be a good foundation for a 408 stroker build

-8 indicates the 8th block cast in that mold..

sonic check it to be sure..

you mean no higher nickel content no heavier casting i got it with a shop full of mopar parts i bought when a bud was moving he talked like it was something impressive

-8 means that casting mold for that block has been fixed or repaired 8 times...

Mopar blocks are all Hi Nickle when compared with other brands..

Yes it means the core for the mold has been repaired 8 times.

The dash numbers mean absolutely nothing as far as the quality of the block goes.

As for your 360, there are no bad 360 blocks as far as year or casting number. The earliest three years '71 - '73 were cast using 340 cores and they supposedly have thicker cylinder walls so they could be better than the average 360 block but all of the blocks are OK.
As in all other Mopar blocks casting shift is the key. It varies block-to-block. Sonic checking is the only way to be absolutely sure and if you are building a 500+ hp engine I'd say a sonic check would be the first thing to see if the block is worth all the time and money. If less power than that I'd roll the dice.
Mopar blocks are made of pretty good stuff so that shouldn't be a consideration. If you want a really stout block then you're looking at a race block or 340 resto block.

R.

I started out in the chevy world where there were supposedly high nickel blocks and also high tin blocks. It is interesting that the Mopar world hasn't started worrying about high tin blocks!