So this one is a B model? I just thought of it as a T01; but sounds like there was more than one T01.
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That walnut beauty looks like a 75U ("Universal") to me. I used to have one, came with a ton of accessories - barrel weights, sight risers, palm plate, sight inserts, very cool gun.
The "T01" refers to the action, and a group of mods made to the initial model 75, mostly to the sights, after a couple years of production. The suffix letters denote stock types and accessories (I can't remember whether these letters also appeared on the action, but AFAIK there were no actual internal differences).
The 75B was a beech-stock model that came late in production, after walnut stocks had been discontinued; as you can see in marflow's catalog cuts, it is a simplifed rendition of the original gun's stock shape. The 75S did the very same thing for the previous 75U.
As marlfow noted, the one action that differed was the rare 75K Running Boar - same basic stock as the U; with wood buttplate, no iron sights, a scope rail that ran full-length from loading port to rear end cap, raised cocking lever end, and a single-stage trigger.
Another variation was that the 75 was made in a true left-handed action - cocking lever on the left, and all other relevant details switched over.