Well talked to Vince at Messicks - nice guy - pulled the part of the shelf and sent me a couple of photos just to make sure we were talking about the same part - it was a sub but looked like a fit.
Unfortunately american greedy capitalist (not Vince) want nearly $600 for a $99 part - so I...
Just added a 555B TLB to the fleet and have started going thru the ole girl. Generally in pretty good shape mechanically, but the electricals are a disaster (why is that always the case with old tractors). Picked up manuals online - working thru replacing necessary and appropriate wiring...