If you are looking to transfer to digital (not concerned with actual projection) you cannot get any better than Vision3 50D for your 514.
Your 514 is going to read the Vision3 50D cartridge as ASA 40, exposing it about 1/3 over. That's perfect for shooting Kodak Vision3 50D. That slight bump will decrease visible grain and bump up your shadows. Also, using a daylight stock outdoors will eliminate the resolution reduction of your internal 85 filter. In fact, don't use it even with a Tungsten stock. Get an external screw on filter. The latitude of 50D is about 5 times better than Tri-X. Even if your over or under by 2 full stops you'll get a decent and very usable image. With tri-x, you'll get garbage. That's important if you have not had your 514 tested and tuned. It's light meter was never perfect in the first place.
After 30+ years, your light meter could very reasonably be a full stop off in either direction. Even when it was new it was not particularly accurate or efficient. Remember that it's going to use an average of the whole area of the image. So, if you have bright back lighting but dark foreground it's going to take an average of the total light resulting in a scenario where neither is correctly exposed. Vision3 50D will be much more likely to give you a usable image in that scenario. Tri-X will give you crap.
If you have a varying light scenario, zoom in on the subject you are most concerned with correctly exposing, get an exposure reading, and then use the lock function to lock the exposure in place. Then zoom back out and shoot your scene normally. This will increase your odds that your primary subject will be correctly exposed and your highlight areas exposed at reasonable levels.
All that said, if you correctly expose Tri-X it's a beautiful B&W and contrasty image. When you get more comfortable with shooting Super 8 (and probably get either an external light meter, tuned camera, or both) it's a lot of fun to shoot Tri-X. Try it while you can, I don't think it will be around for long.