Do it! But, do it all. These were assembled machines using off the shelf components. You are now dealing with 30 to 40 year old major parts. Unless you are a purest and want a perfect restoration. I'd consider the following. Tear it down. You are going to do this anyway once you have decided to change out transmissions. Measure up the available space, weigh the V4 and transmission. Do some kitchen table math on the gear ratios and hit the salvage yards. I probably would stay with a Ford drive train, say something out of a Ranger. this step will eliminate the problems of matching up a newer transmission to an obsolete motor. I'd defer to those who like the brand to offer a specific suggestion. I wouldn't see much point in an OD equipped automatic, you simply won't use the upper gears.The existing radiator should be OK, just work backwards, and the changes in length can be made up in the drive shaft. When you are done you have a EFI engine, parts are on the shelf at NAPA, and you will love how the machine drives with an automatic.