My $.02 -- or maybe more like my $.10 -- on this subject:

1. Based on what I see in how Trick Flow prices their other heads w/ comparable features, I'm expecting them to be $2000-2200 a pair assembled. Not sure if I see a solid roller-type spring option listed, though.

2. I believe I could take those heads, put 'em on my 452 RB shortblock, stick in the 265 @ .050" x .650" solid roller I got from Dwayne Porter, drop on my plenum-ported Edelbrock Victor intake & one of my carbs and make 640+ HP on pump gas, easily enough to put my street/strip E-body into the low 10s. It ran 10.5s w/ 610 HP on Dwayne's dyno, so it looks reasonable to me that those heads and a nice roller would pick it up at least a couple of tenths.

3. They're sized (runner volume) much better for a 450-ish cube application than someting like a standard Indy EZ, because the EZ runners are just tapered-down MW-sized runners. The velocity on the Trick Flow head is probably way better across the lift range than a modified standard-port size EZ, even if the flow #s aren't as good. An EZ is really just a Max Wedge port waiting for a grinder to open up the entry, which puts the CSA and runner volume up to IMO what's much better suited to a 500" application.

4. They've got a better chamber than any that Edelbrock offers for the Performer RPM (or what Stealth & Sidewinder copied), the OOB CNC porting and decent flow #s are reasonable for that size of head, and they won't require any special valve train. If I wasn't already vested in Edelbrock Victors (own one ported set & the requisite offset intake rockers & roller lifters, and have another unported set on hand for a future project), I'd be giving these Trick Flows a serious look... or waiting to see what the "intermediate" set that Brian hinted about looks like.

5. Yeah, they need to fill in that gap on the intake manifold side to let people punt the OEM-type valley pan.