IF someone were to do it, the best bet to start would be to retain the original engine. That way it would really only be focusing on the rear area of the car.
Relocating the fuel tank, adding in a rear differential and making everything line up and work. Would probably work well with an independent rear axle out of an Explorer from a yard, adapter plate off the engine and match it to any desired transmission (automatic to start and keeping things simple) then getting a driveshaft made up, be it . And keeping in mind to keep serviceable items, stuff like universal joints, listed down somewhere and a commonly used part, that way maintenance is easy.
After that it can be enjoyed and a few things can be sorted out to adjust the feel of the car, sway bar sizing, changing of shocks / struts to suit your desires for what you want from the car.
Then you can go crazy with changing the engine for something larger or swapping to a manual transmission. Stages. Projects can quickly become overwhelming when they lack focus. And a large project such as a rear wheel drive conversion requires a lot of attention, so it would be best to focus on the main focal point THEN branch off to the next step.
That's just my two cents tho.