How do you know it was a chopped-down F150 rear end blues_cowboy? All the '77's I know came with the newer style housing, if that's what you mean.
I've always just considered it a running change, rather than having been a modified full-size rear end. Before that, even the older the full-size trucks had the old "banjo" style housings too, so to me it was just a running upgrade for the Broncos, just like the full-size trucks.
I think the full-size trucks got them first, but like you say, maybe Ford still had some of the smaller, Bronco only housings waiting for install so the older style was in production a little longer for the EB.
Typical production thing. Just like full-size trucks got the identical disc brake setups slightly before EB's did too.
Or did you mean something else?
I had also heard that some of the later '76 model EB's got the new style too though. Anybody out there have the later style housing on their '76 by any chance?
Paul