sounds like the cam is installed wrong. retarded cam timing will cause very low pressures like that.
As for heads......I would use a set of edelbrock heads, 64cc chambers, 170cc intake ports. I would also use the regular performer heads with the exhaust crossover (not the rpm heads). This will come in handy when it is cold outside and -30 is pretty cold.
vortec heads are nice and would match your cam very well. be they need special rocker arms, valve covers, and intake manifold and machine work to run a cam with more than 0.450" lift so it ends up costing the same or more. And they flow terrible on the exhaust side.
you should get fairly good performance even with a 2.73 gear if you can make some more cylinder pressure.