If you don't get an engine out of a donor pickup then you will need...truck oil pan and pickup tube, truck engine mounts, a kickdown out of a pre-73 car (3 piece) if using a 727, truck exhaust manifolds (or headers), and of course a BB 727 case or BB 4 speed bellhousing.

You can still get the oil pan from chrysler (cheaper than mopar performance, and it's the same piece) you can also get the engine mounts from chrysler.

The kick down you can find in any junkyard, the exhaust is the toughest part to locate but they're still around, chrysler still has them as well but they're not cheap.

The best bet is to find a donor truck, get all the parts and it'll easily pay for itself. Couple other things, the wiring harness needs lenghtened to reach the coil/dist, and you will need to find the passenger side inlet water pump housing so you can keep your original radiator (BB's came with L or R inlets and they're very easy to find on older cars).

You can pull your internals from your SB tranny and install the tail shaft in a BB case if the original tranny was a non-OD 4x4 automatic.

A "B" engine (383/400) will fit without clearance problems due to the power brake booster on any truck, a "RB" (413/426/440) won't when the truck has the larger diameter booster like those used on light duty trucks. A smaller booster can be swapped to clear an RB, however you need to use the cast iron m/c as the aluminum ones are a different bolt spacing and won't mount to the booster without modification. If a body lift is used then clearance is not an issue.

Jason Hansen has an excellent site that details the above points and much more at http://msnhomepages.talkcity.com/YosemiteDr/xjhansen/swap1.html