I'm not sure that a service manual exists for Montana tractors. Your best bet is probably to use the parts diagram that somebody had linked to earlier and use that. LS does have a little bit of an operating manual if you know which tractor of LS' is a twin to the 5740. According to tractordata.com there are 3 LS tractors that have 57 hp. Only the N53 and N60 have the same engine as yours. A quick google search should yield one of those operation manuals. The LS operator manual combined with the montana or the LS parts manual is all I use with my 4944. I found the loader manual from Ameriquip.
As for your PTO problem. I've had/have a similar issue. Sometimes mine doesn't turn off sometimes it doesn't start, sometimes when it does start, its pretty weak. I took it to the shop and they found a little bit of debris in the valve controlled by the solenoid, they said that valve was giving readings from 100-200 psi when it wasn't working and 215 psi when it was working properly. I brought it home, it worked great for a few minutes then back to the same old problems. After looking at the divider block that allows some fluid to the PTO and some to the rear remotes/3 pt it looked like there was a possibility for an air lock or some sort of relationship between pto and rear hydraulics. I turned the pto on, at first it wouldn't turn off, so I dead headed the rear remotes for a second and then the pto shut off properly. Maybe it was just dumb luck, who knows, but i won't declare it fixed until I test it on the rototiller this weekend to see if it has power. It certainly seems promising though because I had cleaned out that solenoid valve until it was spotless inside and out.