The spacer on the bottom "stump jumper" is 1" roughly on both types I have/had. I bought one for my first drum, the Turkish manufactured one, and the dealer installed it prior to shipment. The spacer consisted of a steel ring, the diameter of the drive mechanism...about 4", cut to 1". The bottom stump jumper (free wheeling disc) is held in place with 3 Grade 8 I suppose, as thy were hex-socket type bolts. With that spacer, cutting crops that could be laid over with the bar that encircles most of the mower (except at the 3 pt area) prior to blade contact, like Haygrazer, could get 3-4" stubble.
Life was short however as I was doing a neighbor's place which was much rougher terrain than my place and I was running at a good clip to get it done, and the 3 bolts sheared. I didn't know it till I was lifting the unit for some reason and the outer stump jumper fell off..... apparently, after it started breaking bolts and became loose it ruined the lower bearing on the vertical shaft. In short I wouldn't recommend the spacer unless running on smooth pastures.
Since the unit weighed 900+# and I have no helpers, I couldn't repair it alone....really needed to flip it over to get at the problem to repair. Sold it for what it was and bought the Tar River 6'. No dealers here in N. Tx. but found one in Kansas who had a $3500 price tag including direct drop shipment from the North Carolina distribution center.
The spacer available for it lists 44 cm.....at 25.4/inch about the same 1" height. One reason I bought the TR was the way they designed the support for the stump jumper. If you pull up parts diagrams for both machines, you will note that the TR has a much better system of supporting the stump jumper disc and I would expect a spacer on that machine would hold up a lot better. Also the mechanism for moving from mow to stow...when you need to do that seems to be more user friendly.
Another reason I bought the TR was the fact that the shield on top of the cutters protrudes farther out front of the discs, reducing the opportunity for throwing rocks at you or your "cab glass" while mowing. I bought a Ford 3910 open station to use with that mower and rigged a piece of plexiglass (Lowes) on the right fender to shield me from flying debris. Works just fine. The cab tractor I keep hooked to my baler.
One note of caution with both. The shield around th belts collects clippings and you can't get them all out without removing the rear (half of the) belt shield. Got tired of that so I just left it off. Nobody around but me and I have enough sense....I think...to avoid rotating machinery.
As it stands now, without a spacer, I cut grass with it and SS with the MOCO. Seems to work for me.