Engine options to put in 67 Dart GT convertible

My name is Matt. I am 18 years old, am a senior in high school, and have owned my 1967 Dodge Dart GT Convertible for almost four years now. I bought the car as a way to escape the world whenever I needed a break from reality, which I was very desperate for when I first heard that my mother was diagnosed with stage 4 lung cancer. We agreed that getting me a project car would be the best way for me to be able to work with my hands, which is my way of escaping for a little while. However, being a freshman who hadn't even gotten his permit yet, my mother told the older guys (in their 40s and 50s0 in my small car club to only show me cars with six cylinder engines so that I would't kill myself drag racing or something like that. I now realize how right she was, as I have not always been the slowest and least showy driver on the street. So I rebuilt a slant 6 225cid from a 1972 Dart Swinger, rebuilt a transmission to go with it, and replaced the reared with a refurbished 8 1/4 because it was the only free option at the time, being the only rear end we had lying around our parts and work yard. I put all of this in along with countless other little modifications and serious ones as well, including: front Wilwood disk brake conversion, new slant 6 A/C car radiator, high output alternator, new p/s pump and box, all new front suspension, some rear suspension parts, tires and wheels, interior parts, and hundreds of other small jobs about three months ago (which took a total of about 8 months to finish). However, now I am realizing that this car deserves more than a slant and stock 3-speed setup for a powertrain. Also, I'm tired of not being able to keep up with everyone else on cruise nights and regular outings to the point of embarrassment. I'm ready to start setting up a V8 swap for the car, but I have hit a couple road blocks. The first problem is that I do not work during the school year, so I am pretty strapped for cash. Usually I can scrounge $25.00 a week from my mom for doing odd jobs around the house, but rarely much else. My second problem is that I have no idea what to look for in terms of engine/tranny options. I know, being a convertible, it wouldn't be the best idea to put something like a 440 in the car, but I was thinking of going with a small block. Maybe a 273, 318, or 340? What do you guys think?
Sorry about the long post, I'm not great at shortening stories and questions.