(2)450 DP's vs (2)750 DP's

Absolutely no idea. I have one and only one experience with stealth heads and it’s on @Turbo440Dart Chris’ car. I was there when it was tuned on the dyno but have no first hand knowledge of the timing curve it left with. My guess would be they are possibly a bit better than stock 915/906 chambers but it’s a guess at best. What does the strap on your spark plugs look like at your current wot timing?
To be honest, I don’t have a place close by I can really run that type of test. No tracks close by and the closest doesn’t have a test and tune time that I’m able to attend at this point. Next time I make a wot run I’ll see if I can scout out a decent location to do it.