5665 questions

So, the old LI has been sitting out under the porch while we tinker with it and try to get it going. Yesterday the neighbor stops by and asks if want another one.

Another one? They multiply??? :sidelaugh

We go over to his barn and there is an old 5665, circa 1990? I'd guess. It started right up, but I have two questions -

First, when you pull the PTO lever it engages with a bit of a grind and clunk. He has both the gear select and the forward -reverse levers in neutral and it still doesn't sound real smooth.

Second, the PTO engages and runs normally when there is no real load, but when you attach the 50" deck and try to cut high grass the PTO slows or even stops. Is that likely a misadjusted slip clutch?

His father left him the machine and deck, as well as a chipper, dump-cart, and a snowblower, but he hasn't used them. He's willing to trade me the equipment for some 3 point attachments I have been looking to get rid of, and some old Corvair parts I have had for years, but I just started with these machines and I'm not sure I want to do it.

Any thoughts would be welcome!