A mint complete black interior is worth over half the asking price by itself. I'd go for it. You can change a tranny in your driveway if you're a glutton for punishment, but it doesn't require much skill or special tools- just awkward. I'd buy a new one unless you know someone who'll give you a deal on a rebuild, T5's are cheap. If you're serious about that 331 and the numbers you're talking, you may as well spend the money now on a Tremec and be done with it. You never did say how it runs? Immediately having to dump a bunch of money into getting it to be reliable really cuts down on the budget for the other stuff you mentioned. You can have a Maako shoot it blue for under $1000, it's all in what you can live with. You get what you pay for. If it really needs work too look good, you should be able to talk them down some more since you can't even drive it without grinding gears. Good luck!