By looking at it that is a very nice car. I would keep it, and it'll be fun to rebuild the 289. Putting some mods on it and you have a fast little fastback.

 

what state are you in? i am here in southern california and just got my short block built for $500, almost all stock. I paid $85 for my cam kit from summit and a double roller timing chain for $42

 

Hey welcome to the forum, I would definitely consider myself a mopar guy too.. Just so you know, you're just motor mounts and a harmonic balancer away from putting a 302 in your car. I bought my 64 1/2 and the first thing to go was the old motor. It took me all of 30 minutes to get the old motor out, and putting it back in is just that easy. The 289 and 302 are interchangeable, as well as putting the intake on, although I'm not too sure about the exhaust. That is DEFINITELY the easiest way to go in my opinion, plus the fact that 302/5.slow's are a dime a dozen. The only thing you'll need to worry about is the balancing. Mustangs Plus sells the correct weight harmonic balancer that works with the 3 hole pulley. Expensive at almost $200.