Tentimes, one of our members, aldot, has a Tractor 11 and can probably tell you the answer. If he doesn't join this thread you could send him a PM. Here is the chain drive on another member, KeithB's, 11-28:

[Linked Image]

The chain does look rather wide, but of course it may not be the original part - fitting wider chains and matching small sprockets could conceivably be a popular modification. However in the case of extreme chain drive ratios like that, I suspect that having a wide small sprocket might greatly outweigh the wear-life advantage of having the chain match the width of the large sprocket. I don't think we have ever had a completely worn-out large sprocket reported here.