Mechanical Sympathy

Actually yes, as Reed suggests - I forgot you have more options in the states. Depending on how much you want to spend, a T-series crossmember and engine conversion gives you a 5 speed almost by default and the option to go twin-cam.

I heartily recommend a 5k or even a 7k transplant, if you can source them there. We got them in LiteAce vans here. A 5k with extractors, 1 3/4" exhaust and (standard on the 5k) electronic ignition offers a significant and inexpensive improvement over your 3k. Bolt on your 3k flywheel/clutch/gearbox and manifold/carb (so you don't have to adapt emissions controls from the modern engine) and away you go. There are faqs/wikis on the front page that go into more detail. A 4AGE doesn't directly fit and will cost three times as much by the time you're done - think engine mounts, rear wheel drive conversion, gearbox/clutch, gearbox mount, tailshaft, wiring loom, efi or carbs etc.