Best guess on 434" sbm

She is a little portly...lol. A lot will have to do with how the convertor works too. IMO, 4500 is a little low IMO but this is a double-duty car, right?
I know the pistons are worth something. Are they low tension rings? gapless top? My impression is you'll be on the edge of enough horsepower - which only means the chassis and convertor are more critical. I think you can hit your number - it's just how much faster. Not knowing the details on the camshaft either - I'd like to see another .050-.075 lift and another 4-5° @ .050 to really use the heads.