FT and SuperDuty warrenty...
I worked for Duthler Ford (car and truck), in Grand Rapids MI, from 1969 to 1976. We bought new (FT) 391 and 534's from the local Cat. dealer, and delivered them to (mostly) West Michigan county road "commissions". They were probably (mostly) replacements for dump trucks, and came with a 100,000 mile warrenty from Ford.
They were industrial versions, on skids, and complete with bellhousing and double disc clutches (on the 534 for sure).
For some reason, we could buy them cheaper from the Cat. dealer than directly from Ford (probably a volume purchase thing).