I've shot an AMT that had been converted but never a Swiss 57, semi or otherwise. The AMT was lots of fun and recoil was much more tolerable than any G3 I've ever shot. The AMT recoil sensation had a sort of rocking motion to it, if that makes any sense.
Passed on a PE57 in 1982 NIB with two mags for 2 and regretted it many a time since.
Last one I saw was at a show about 6 years ago. Same deal, NIB with 6 mags, sling, bayonet, and small parts kit.
It had a P.O.R. on it which I thought was a rather strange way of pricing a gun at a show.
I had 4500 on me so I thought 'What the --, let's just get it'.
I was reaching for my money as I asked the price. 7500.
Ouch! Being told no hurt.
It sold within the first hour of the show.
Good luck with your project, JT