If you just made them all to the 24.5mm compression height, and with 1mm deeper valve reliefs, couldn't you just have the ones you need at 23.5mm faced off to that from 24.5mm?
Also, a note of caution, you may want to measure your piston height at TDC to the top of the liner for each engine. You may need something other than 23.5/24.5 mm to get ideal quench. That's the part I missed when selecting parts for my 660. I thought I'd need a piston with 23.5mm compression height (stock for the 600) to go with the custom Carillo at 130mm (stock for the 600). However, if I had done a better job of measuring when disassembling, I would have found that I needed a longer rod. We ended up switching to a KTM 560 SMR piston (24.5mm) from the 'Berg 550 Wossner I had originally purchased for the project (23.5mm) and then Travis still had to deck the cylinder down and install a manual cam chain tensioner to get the quench into a reasonable gap but still have enough throw to tension the chain.
My plan for the 501 (to turn it into a 606) will be to use your piston and design a custom Carillo rod to accommodate it based on careful measurement at disassembly.
Oh, and I imagine that I could just cut down one of your sleeves to work in the 501 cases? Maybe I should commit to buying one of those as well.