One thing that makes a big difference here is your cam, do you know what you have? A cam selected for a those heads and compression may not preform as expected when you swap a different set of heads on there that make their power in a completely different RPM range.

So what we are trying to say is what is the purpose of having a higher compression is it just for bragging rights or do you want more power if you want more power how much do you want?

I think for now get the car and drive it and see how you like it and go from there.

As far as your 302 comparison well, The 302 with dished pistions what kinda cam is in it how many miles are on it has it been taken care of is the distributor properly curved or is it all stock? Same goes for the flat top piston motor if there has been work done to it well of course it would preform better then a stock setup, not really fair to compare without any information and if they are not built for the same thing then you also really cannot compare.

Anyways sorry to repeat myself but get the car enjoy it and see if you want more power if so pop back in here and we can help do you have any other build information on the 351c or just that its got 2v heads with 8:1 compression, also how do you know what kind of compression you have? I would try to get some information about who built the engine and ask them anyways take it easy man dont mean to ride on you just trying to save you from not being happy with your ride and or wasting time and money everyone knows we need it now a days with gas prices.