11:1 is WAY low from what you'll have...
with zero deck, 0.04" gasket, 64cc head, and 4vr (guess @ 6cc) FLAT-TOPS will give you 11.5:1
Start adding a dome, and you're soaring into mid 12:1! With the cam you mentioned, you'd have to run race gas.
Granted, a 400 does need more cam duration to feed the cubes, and that duration will need additional compression to give a good crankng psi, but not that much...
With a 10-15cc dish, you'll be right around 11:1 with a 64cc head. Then run a cam in the 245-250@.05 range, but with a slightly wider LSA than usual (like 112+). This will give you a later intake closing to keep cylinder pressures under controll.
The old LT1 cam, or factory 'off-road special' would be good cams for a street-driven high compression, big cube motor. Just run high ratio rockers, because those cams run kinda low lift...
To answer your question about the head flow, I agree. Flow tests I've seen don't make the RPM's look very special at all - maybe a bit better than world S/R torquers (which have the same runner size BTW)
With the high compression the RPM heads will give you, you'll have to use a larger cam to keep away from detonation. BUT the large cam is going to want higher rpm's, which the Eddy RPM heads won't be able to support...
If you've got them, run them for now, but save for new heads as soon as you can.
Something with 200cc runners at least (World, Dart, Pro Topline all have good heads for a budget in this range)
Also, when you're buying new heads, you need to decide on chamber size.
On the one hand, you can buy larger 68-72cc heads and run flat-tops with a reasonable CR.
But, OTOH, you could also get dish pistons, run 64cc heads, and have the option of putting larger heads on later to drop the CR, and running a blower/turbo!
I'd go for option 2
They also say that the small chamber/dish piston is more effecient... (as long as the piston still gives quench area - a 'D' dish - we're not talking stock bathtub pistons here!)