A free bike is a good bike, even if you have to make a few changes.
What is your budget for this bike? My recommendations, and a suggestion of adding a pinch of salt:
- get the bike fitted to you, for triathlons. If you're planning on using aerobars, adjust for that too. I've found that with my aerobars, i need the stem at a slightly different height.
- get some nice, lightweight wheels that will work well for racing, and possibly training, depending on your budget.
- what type of rear hub do you need? freewheel or freehub/cassette? Depending on the courses you plan on using, selection of gears will play a part.
- If you go with a modern freehub/cassette, you could upgrade to modern integrated brake/shifters. Or, depending on the aerobars you use, some will let you install barend shifters. Otherwise, practice with the downtube shifters.
Enjoy the Prelude. I sold one a year ago, and still miss it. It was a nice bike.