compression = horsepower query

Guys,
the pics are from 2 years back when i built the motor, its fully assembled currently and runs well. I checked the Federal Mogul site last night and could not find the dimensions i need (the valve relief cut out x cc) on the pistons.

Having read about 30+ posts on 'what cam' etc, I suspect i could replace the current XE262 cam for the 268 version, which would put some more power in.
I'm also changing the stock convertor for a 2800 stall.

I dont really want to cut the heads too much or i'm into cutting the inlet manifold as well.

You know how this works, Winter comes around and we /I start to think about rebuilds more power etc...limited as ever by budget/practicality etc..

longone, didn't know there was a .019 gasket, who supplies those?