My 514 engine had EZ heads on it and it made over 900 hp several times. Here is a super long thread on that engine if you want to look it up: https://board.moparts.org/ubbthreads/ubbthreads.php/topics/804381/14.html
Chuck said I should've tried more ignition timing so that is one thing. I also had the AFR at 12.8 which is safe. We could've leaned it out a bit. We were using C12 which is a decent fuel but there are other fuels which can pick up power. Bigger headers would probably make more power. PipeMax says the valve lift need to be higher. Right now the intake is choked because of the low lift. We didn't want to go with Jesel rocker arms on these heads so we are limited by the shaft rocker in what you can do. I'm sure there is more power in the valve train but not easy to get to in this configuration. Switching to Jesel rocker arms on my old 514 was key in picking up a bunch of power. Also, if this was my engine I'd switch over to a belt drive distributor. The belt drive distributor is more stable which means you can safely creep up to the limit with the timing.
My 514 started out as a 750 hp engine but after a 100 dyno pulls we had it over 900 hp. Same basic long block combo, just changed the cam a bunch of times, ported the intake, switched to Jesel stuff, etc.