Your adjustment is in the length of your belts. Keep them tight and you'll make tighter bales (says the rancher who ran with a sloppy center belt and slack outer ones all summer).
They are a pretty simple machine. Ours was new in '72 and picked it up from an uncle used in '74. About 25-30,000 bales through it and still hums along. Bent the pick-up on it this year though...still made 450 bales.
Nothin' prettier than a red Ford truck, a Massey Ferguson tractor and a red-n-white Hereford sittin' on the farm.