Join Date: Jan 2019
Location: Sedgwick, Kansas
Pistons are important, but you're not going to 'gain power' by changing pistons. So long as they're strong enough to take what your engine can dish out, and they offer an appropriate compression ratio, then don't mess with 'em.
You can argue that well-designed lightweight pistons that match your heads can deliver more power, but there are much better ways to chase a few horsepower. This is something you worry about when you put in a new crank and rods, or build a new motor - not something you mess with if it's running as well as yours does.
I'm betting these are the ubiquitous Keith Black flattops with some little eyebrows for valve relief. +6CC or so to volume, but they should give you good quench and adequate valve clearance, so they're not a bad choice.
A tailpipe sniffer really isn't that handy for telling you what's going on in the engine, by the way, so don't feel too cheated. They're useful for reducing emissions and tuning for economy, but they won't do much for chasing power. You could be blowing a lot of unburnt fuel down the header along with a lot of air, and continuing to burn in the exhaust. Sniffer might say "No problem!" but your O2 bung in the header would know better. (obviously, your engine is not doing this; I'm just creating a fictional example here.)
Anyway, all this to say first: if you really want to make a substantial power improvement, you've got to do it with breathing. Heads, cam. You already have an excellent way to get air in, and exhaust out, so don't mess with those.
The only other way you could significantly increase actual power would not raise your horsepower number. Stroking your engine would gain you a lot of torque, and lower the RPMs that you make peak power at. This would help your lifters (because they don't have to deal with the higher RPMs), and decrease any mixing problems you're having on the bottom end with your big 750. While it will usually hurt your mileage a bit (especially if you can't keep your foot out of it!) running a 331 or 347 will roast tires and create a lot more power under the torque and horsepower peaks. If changing the stroke is the only thing you do, it typically won't raise peak horsepower, but you'll wind up with a lot more average horsepower.