I have always used wallace and thats fwhp with whatever set up you have for weight/mph, always comes out a tad more than the slide rule.....example>

Our '69RR, wedge motor dyno'd@695hp
3800lbs@line, through muffs to rear
all mechanical w/pump/alternator, street set up
with air cleaner.
Wallace shows 10.35@129 as 677fwhp on track...1.42 60's best so far.
Which is approx 20hp down from dyno no's which used same carb.