First of all, let's get something straight. Any Sealed Power or Speed Pro piston with an "h" in front of it is a hypereutectic piston. So the H116CP as well as the H405CP are both hypereutectic pistons.
Second, what heads are you going to be running? That's a huge question. Open chamber heads and closed chamber heads have different needs.
One major advantage the KBs have is they are light. The 107 is 507 grams and pin is 132. Sealed Power/Speed Pro pistons are usually stock weight which in this case would be 584 grans, plus the thicker wall pin is at least 152 grams. That's at least 87 grams off the piston/pin assembly.
I'd suggest going to the United Engine and Machine website and look at the choices and their weights.
Keith Black pistons do require larger ring gaps, especially the top ring. This gap is usually big enough that one can use regular rings and file fit them.
Do look around on ebay and other places. For example I found a set of forged pistons for 4" stroke 360 for $315.00
Good Luck!
R.
Didn't realize the Speed Pros were close to stock weight. KBs are definitely lighter and will necessitate a balance job on the rotating assembly. Something else for the OP to keep in mind.
The KBs definitely need the larger gap on the top ring. I've read elsewhere this is a lot of the source of negative feedback in KBs, user error. People put them in with stock end gap, ring s heat up and ends contact, ring keeps expanding until it wedges into the cylinder wall, top of piston cracks off. I've always used off the shelf rings and hand filed the gap on the top ring myself. Just takes a little measuring and some careful work with a fine file. Formula for necessary gap is on their website.
