Push button dash

I agree with C130Chief, unless the front pump seized (which I've never seen happen), the trans is not the problem with an engine that won't turn over.
As for the push button assy, make sure the cables move free and easy. Then spray the shifter assy with WD40 and see if it shifts in all gears without any buttons binding in or out. If the park lever just flops, it's usually just the over-center spring. It's fairly common for those to break. To use an aftermarket shifter, you have to change to a later transmission and driveshaft because your current trans is a 2 cable internal type setup whereas the aftermarket shifters are setup for a single external cable.
Good Luck, Mark