Paul, the rear truck is an oddball arrangement. It has a single axle, and then two tiny "pony" wheels. The pony wheels are an attempt to steer the driven wheels. Adjusting the tension on the arm that rides on the chassis, not to mention getting those pony wheels to turn freely, was an interesting exercise. If everything is not right, the pony wheels hop out of the rails and of course that stops the music. 
Of course, as luck would have it, the rear truck also supplies most of the tractive force as a rule, so it's critical to get that balanced for proper operation.
I've toyed with the idea of hacking the rear truck and fixing the wheels straight ahead and losing the pony wheels. That might be a problem on tight curves, but on wider curves I suspect it would probably work. I have not been successful in finding a rear truck for the locomotive so I have something to experiment with. I don't want to hack up the truck I have in case my idea is unworkable.
On the Con-Cor N-scale Aerotrain loco, the front truck is 2 axles and powered, with traction tires, and free to swivel like a normal diesel. The rear single axle is unpowered, no pony wheels, and free to swivel, in order to take curves better. As a matter of fact, all of the trailing coach cars have single axles that also swivel, for the same reason - to allow them to negotiate curves better. Sounds good, right?
WRONG! Those swiveling axles are one of the BIGGEST boo-boo's on the N-scale units, from the rear loco axle to everything after that. While swiveling axles may have looked like a good idea on the drawing board, in reality the problem is that there is nothing to control which way they swivel. For instance, they may swivel to the right just as easily as they swivel to the left when going around ANY curve, left OR right. Or even going down straightaways. Which also means they do an excellent job of picking points and picking frogs and derailing in general whenever going through turnouts, no matter which direction.
I locked all the single axles (loco and cars) to the straight position where they couldn't swivel anymore, and that took care of poor tracking characteristics of the train. After doing that it went around curves just fine, through turnouts with ease, and straight as an arrow on straight track. There were a few other problems that needed solved too, but they were diminutive N-scale problems that wouldn't affect a good, hefty O-gauge train.
At any rate, without actually having an MTH Aerotrain to look at and study, I'd be willing to bet that fixing the rear axle straight ahead and losing the pony wheels would probably work, just like you're thinking. I'd even be willing to bet that it would be just fine going around tighter curves, too, let alone broad curves. I'm generally not much of a gambling man, but what the heck - since we're talking your locomotive and not mine, I'll go ahead and bet anyway that it would be just peachy-dandy!!! 
