[qksilver]

It would be better to go with the newer frame. easier , much less work, if i remember correctly the burb 's wheel base is a little bit longer, I think 1 1/2 inches not hard to make up between the bed and cab.
I have done a couple of frame swaps from 55-58 trucks onto 67-72 frames. Fairly easy , I removed the cab mounts from the old frame, measured and drilled and bolted them on to the new frame. Not a major deal, I think the frame widths are very close on the 64 to the 84.
The other way would be to use all the brackets off the burb, spring perches, transfer case etc and measyre drill and bolt them to the 64. The 84 engine crossmember will bolt in so that is one less head ache. With the 84 cross member you will have clearance for the front axle,exhaust and engine, better motor mounts.
The 84 has longer rear leaf springs than the 60? to 72 4X4 and the rear axle spring mounts are a different width. P/S there isn't a dimple for clearance of the Box so it won't mount flat to the frame. You can buy a bracket kit for around 75 bucks or heat the frame and dimple it.
If you are getting the complete Burb you can rob pretty much everything off of it and make it fit. I am kind of doing the same thing with 87 3/4 burb parts on a 68 4X4 1/2 frame.
Use the wiring harness, the gas tank........every thing you can, save you some money and have parts that work together from the factory.
Steve