65 driveshaft possible upgrade

To clear things up, this is already done. The engine and transmission are together, running and driving. What led me to ask questions are that the shifter cable(s) are leaking (we believe) and before I sink any money into this transmission (new cables, etc.), I want to know if I'm dumping money into a dumpster or if this thing (mainly driveshaft) will live. I had a friend who had good luck with the 904 and I don't plan on big HP numbers. I dropped the trans pan yesterday and the fluid and the internals look very clean. It's just the big leak that started a few weeks after parking the car is what has me concerned. It looked like the fluid was running right down one of the cables. New ones are over $500:(
Not that I wouldn't spend the $$ but I just don't want to do that just to replace the whole thing later on due to a driveshaft that won't serve its purpose.

Thank you all for your inputs and if there is any more info, I'm open to it.:thumbsup: