If the 308 TH engine has good compression and runs, if I was you i'd do the following:

Make it look original like you say.
Buy a whole VN-VS 304 and 4L60/4L60E. You'll get one of these for under $1000.
Buy a new EFI cam.
Strip the top end off the TH308 and put the whole EFI top end on it, plus the new cam.
Put it in the HJ with the 4L60/E.

Pretty much bolts in like any other 308, plus some wiring and fuel muck around. From memory a TH400 tailshaft with a tonner yoke goes close, you can all but use a TH350 crossmember (or make it yourself), TH400 speedo cable and T-bar both work.

There is a few things you have to buy like speed sensor and probably a low pressure lift pump plus a swirl pot. But all worth it in the end as one of these with the 3.08:1 diff will be pretty economical in a relatively light vehicle like a HJ van (or use the 2.78 if you want small diameter tyres).

The reason for using the red motor is if you use it there is no need for any Engineering, just the same as putting a Holley carb on a HJ. If you wish to go this way let me know and i'll send you some info. There is really no point in trying to date code match etc as you don't have the original engine.