Real world swap cost
I have a 4speed that needs some tlc($$$). If you decide to go with a 4speed I would donate the 4speed and the labour to rebuild it. I would have to look inside of it and we would have to price the stuff out. I am guessing but, to do it properly it will need somewhere around $500-$800 worth of parts. There is a place in edmonton that has alot of parts for these (NOS jobber type parts).
If I were you I would do the swap. You can make it look factory quite easily. I also have a pattern to cut the hole in the floor for the 4speed hump. I did the swap in my 74 and have learned a few of the pitfalls.
Also don't forget you will need a new front carpet.