^ I haven't built a new aluminum mk65 but the cast iron ones used to take a lot of clean up, shimming issues, etc. They were pretty reliable even when built wrong. I dunno about the new ones, saw some chatter on here about them shipping with the wrong piston, i dunno if they got fixed or what?
The 45mm airsals i've built were a long time ago but the quality wasn't nearly as good as the 44 and going off memory they didn't tune in as nicely. I might be confusing it with the Kstar where they had that tricky low-midrange hole in the power. If i was going to build one i would case match it and not just slap it on. I'm sold that the 44 airsal is the best slap on kit because its so forgiving tuning and setup wise, you don't have to case match, and its not gonna spin fast enough to blow out a brass bushing on a conrod.
I haven't put a PP kit on a puch in probably 5 or 6 years? About half the kits out there are new and half the ones i used to build are discontinued. Nice to hop back in the game and have something just work right out the box.