Here goes, 406 forged dish 10.25-1 compression pistons, gm fast burn aluminum heads, gm vortec high rise dual plane very similar to performer rpm, comp cams XE284H cam, gm self aligning roller rockers, headers are 1.75 long tubes, 2.5 inch duals Xpipe and 40 series flows. Car is 69 or 70 camaro with 3.31 gear in the 69 and 3.73 in 70 RS. Trans is T-10. Will i have at least 350 horses to the rear tires? What kind of engine power? My machinist says to go with a single plane victor jr.

440 Horse estimate at the flywheel minus about 20% drive train loss if auto (maybe 15%)
equals about 352-374 horse at the rear. Just my guess. Wait for the more experienced guys to critique the combo. Tune, tune, tune.

With the auto around 330rwhp and stick around 350RWHP. Should run great!

How much nitrous should this hold? It has eagle H beams and forged and balanced bottom end. I suppose the block is the weak link.

The block may or may not be the weak link. I occasionally spray 150 HP on top of 525-550 HP and the block has been fine. If you have good forged pistons then you will probably be OK.

Truth be told, what usually kills a small block is a valve train problem that causes some type of valve to piston contact carnage. So it's very important to make sure you have proper valve train geometry and proper springs. You could always split the block or blow out a cylinder wall, but probably not at your HP level.

PS. I think the T10 (or maybe rear end) will be the first piece to break with a mild N2O shot (like a 125 to 150)