So it's bored to 4.34 which 4.342" is a standard 400 B piston. so is it probably/presumably .092 over?

If it's an aftermarket KB piston it is probably near zero deck so it might be a snappy performer. If it's a stock low compression piston, probably not so much.

It's an odd-ball size (for that compression height) for anything other than a 400B, isn't it?