If it is a strong engine I would do a compression check. Since you say it doesn't burn oil don't rebuild unless it needs it. Fix the leaks and drive it. Save your money and when it does need rebuilding you should have enough to do it right. If it turns out to be a 360 it would probably be a good idea to change it to a 390 when you do rebuild it.

The 360 will have a 3.50 inch stroke and the 390 will have a 3.78 inch stroke.