My 1969 Chevrolet C-10 Short Wide Bed Pickup

[68Gold/white]

Most things depend upon your budget. Moser will build you about any type of rear end you want, that will bolt up to your stock suspension, 12 bolt, ford 9", Dana 60, what ever, costly though.
Disc brakes won't be a problem either for the stock 12 bolt. The rear end info you've been getting may not be all bad, but it would take a boat load of $$$ to make either work, and your stock 12 bolt is already stronger than those 2 whimsical ideas.

I have a 67 and 68. Neither are running at the moment, however both will have stock type front disc brakes. The regular old single piston stock Chevrolet disc brakes work very well! No need to spend $$ on ANY thing exotic. I hate drum brakes, especially on the front, but plan to use the stock type drum brakes on the rear of my 2 pickups, It would be nice to have rear disc, but it's simply not needed. It's more of a prestige thing than a real drive ability or performance step up.
There's better converters than B+M. Continental custom builds each unit to your specific vehicle, pricey but worth every penny.

I don't know anything about the folks you mentioned concerning the 454 engine. GM makes some awesome crate engines. Scoggon Dickey is in Lubbock, not that far from you, check their website. Some of their stuff comes w/ a warranty.

You can buy 5 lug axles for your pickup from Moser for $260.00/pair, that's a bargain, after buying the axles, all you need to do is buy a pair of 71 or 72 drums, all the shoes, cylinders hardware are the same.
There's probably a differential shop that can re-do your rear end with the gear you desire, and a posi unit, somewhere close to you....

Billet Specialties makes some awesome big block valve covers. FYI!!!