I have not ran one with Cometics with O ring grooves in block, but I have heard of multiple people doing it with success. I would just make sure you run proper size gasket so fire ring is seated on nice solid surface in between O ring groove & bore & should be OK.
Pistons .050" out of hole? Custom pistons? Just curious why you had custom pistons made to be .050" out of hole & what head gasket thickness you gonna run? After thinking about it, I'm guessing you're using open chamber 340 style E heads & that's reason for piston .050" out to get quench with the open chamber, I'd be real carefull to make sure that the chamber is bigger all way around than the bore of cylinder & take intake account piston rock..... assume nothing, measure everything. Bolt heads on bare block & look up from underneath to make sure piston will go into chambers & no parts of chambers are overhanging bore....If that is what you are doing, I'll just give my
that it would have made slightly more power to run piston at zero deck & cut heads to make them closed chamber but that's just what I would have done, would make little more power/have better flame front/propagation & quench by making the heads closed chamber.
Sounds like should certainly make more power than it did before.
Looking at 9.90s 
![5033622-FRONTLAUNCH[2].jpg](/ubbthreads/ubbthreads.php/ubb/download/Number/26360/filename/5033622-FRONTLAUNCH[2].jpg){kind=link}