what problems might i run into with the high lift hydrolic flat tappet? the heads are closed chamber and the compression is 10.5 to one i will use a head gasket that gets me close to .035 for quench. is there any major issues with my combo?and what hp do you all think its good for. i will also end up running a 3600 to 3800 stall converter and 430 gears in the 8 3/4 spinning 27 inch rear tires

Screamer means high RPM... hydraulic flat tappet means maybe lifter pump up issues at high RPM. I believe it is both and art and science to get a hydraulic to work >6000 RPM. It depends on heads and cam and RPM target.

That said, screamer small block screams for a mechanical cam. I may be biased but see no advantage to a hydraulic in a high po application. Both hydraulic and mechanical need adjustable lifters and I think setting valve lash on a solid is easier than dialing in pre-load on a hydraulic.