What Carb for Poly Stroker

Look at the overall combo & remember what you built the engine for: predominantly street driving.

I could you build a great performing TQ that will tear your head off when the secs open...& give great economy. But I ain't going to Qld to dial it in for you.....

Your cam is mild-ish, only about 8* more 050 duration than the 340/275 hp cam. That is going to limit top end, getting pretty tired by 5000 rpm. So why put on a 6000 rpm carb on a 5000 rpm engine? Throttle response & mileage will suffer.

Holley's [ & clones ] are best left in the box they come in.....

The ideal carb for YOUR combo is the 625 AVS2. It will bolt on directly without an adapter. A 800 AVS will not fit without opening up the bores in the man...or using an adapter.
Your 600 H has 1 9/16" pri & sec bores. The 625 AVS has smaller primaries [ 1 7/16" ] for better throttle response & bigger secs [ 1 11/16" ] & has more total air flow. I have only heard good reports about the 625 AVS2. Edel changed the design of the AVS from the original Carter design which was a positive move in my opinion. They added venturies to the secondaries, originals did not have these.
I have been involved with the install of two Street Demon carbs. One worked well, one had a flat spot that was never able to be overcome, even with ph calls to Holley tech.