365 Heads on a 390 Block?

[charles in Dallas]

I have come to find out that my car has a 390 block with 365 heads. The heads look fresh, but should I look for some 390 heads? I dont mind missing out on 7-10 HP from not having the 390 heads, but are the 365 heads on a 390 making less power than a stock 365 because they are miss-matched in the wrong direction? I know you normally put bigger better breathing heads on block not smaller ones.
What happens to compression?
Would that affect how the car should be timed?
THANKS!
Charles

[fishnjim]

You should hook up with the guy looking for 365 heads and can't find any.   This is surely one reason why.   
Without looking, the 365 head might improve compression a small amount.   The 390 was mostly 365 stroked, if memory serves me.   Slightly larger cylinder bores.   The valves might be slightly bigger as the carb was larger cfm in '59s on.   
If it was done right, I don't see any issue as if there was, it wouldn't have got this far.