Didn't see this first time around.
I got the same machine, same problem with the gathering wheels. I took all the old rubber off and got a 16" steel wheel at the junkyard. Cut the bead areas (2) off the wheel. Got a 16" tire and cut the sidewall in a sawtooth pattern, then fastened the tire section to the steel of the gathering wheel using the bead section of the wheel to hold it in place. Worked ok, I'd give it a C+.
Issues were:
Sidewall of the tire wasn't as stiff as it could be to work well. 2nd pass I'd get the stiffest sidewall tire I could.
16" was ok, but a 17" would probably fit better.
The place I drilled for the bolts to hold it all together happened to be right through the steel of the tire bead - that was nasty drilling.
So at some point I may try this again, taking into account the issue above. But what I got is definitely better than it was. I can post pictures if you like, too bad as I had the baler here at the barn doing some repairs, just put it back in the other barn.
As for rear wheel spacing, the largest problem I have with this baler is the narrow pickup - it's between the baler wheels, not out in front as most are. It takes some real care to make sure the windrows aren't too large. So you're going to want smaller windrows anyway, 40" spacing sounds pretty narrow, but I'm betting it'll work for you if you keep the windrows small.
