I would not put a vacuum secondary Holley on that motor. I had a 1000 cm pro system 4150 that was built for our 464 race motor. When I put it on stk 430, same ported stage1 heads and intake as my 464, smaller .500 lift can with lots of duration, 4.10 gears I just had to down get a few front and rear. It flowed a true 987 cfm Never had a choke, would start on the coldest winter days in my garage with not heat in it. Did have to cover the throttle a little at first. I would second a 950hp. Just make sure you double check and make sure the base plate has the ports you need for vacuum. I would not hesitate to call Patrick at pro systems and have one built, but will be more money than a 950hp. The ultra hp are nice they have an air bypass valve that help daily in radical cams. They are more true to flow than the hp due to having a 1.600 venturing size https://www.holley.com/products/fuel_systems/carburetors/ultra_xp/parts/0-80805BKX
The bolt pattern for the qjet is on that manifold and it's the same manifold used for the qjet,..just opened up for the larger bores. You can do it yourself just pack the intake with a old t shirt,..place the qjet gasket on the intake,..mark out line and use an aluminum burr and vacuum to open it up,..or if it was me I would remove it modify it then bead blast it to freshen up. But to be 100% honest as much as I like a good running qjet,...a 850~1000cfm mechanical Holley will perform better with more predictable characteristics
If you check out Craigslist , new York state , oneonta . And search Holley my stuff comes right up . There's an 850 DP with billet metering blocks I have on there . But , I think the dissatisfaction with the Holley vac sec carbs may be with the stock spec vac sec spring , that usually probably don't get changed because they are a pain . The OEM spring is "plain" and on a Small Block v8 the secondary is not fully open until about 8000 rpm . A little bit better on a big block . That's crazy . The purple spring is a little better and the yellow is a step better than that . The quick fuel adjustable vacuum sec assembly I like comes preset with the purple spring . I've used a couple and they seem fine as is . The quick fuel assembly is $24 ( basic ) and a new vac sec diaphragm is $8-$10 so on a rebuild it's only an extra $15 or so .
I didn't see the 850, only 750, and some of your other carbs. I'm running between 10 and 12 lbs vacuum in drive. Also I want to thank everyone for their replies,suggestions and support.
