I would say the easiest and cheapest way to get mobile and still remain focused on what your long term goals are for the wagon would be to pop the hood, remove the radiator hoses and drain the fluid, remove the air cleaner assembly, remove the rocker cover, check the rockers for excessive play then remove the head and check it for cracks, or rust stains around the water jackets, if it looks ok and you are willing to lay down about $35 on a new gasket kit you could try replacing the head hasket and see if it will get you going, at least you know your only going to lose $135 if it doesn't work and you don't want the car anymore, but if it does work then you can start enjoying the car now and start planning the big A15 transplant