You have two 1990s Giants that you want to upgrade, and you have a budget of $300 (misc parts) + 2 x ($600 per wheelset/tires) = $1500. Did I understand correctly.

I'd recommend that you sell both Giants and pool the budget. For $1500+, you can buy some spectacular vintage horse flesh. Get a Cinelli or anything that suits your fancy. How about a Paramount? Just a casual rider? Why not a Centurion Pro Tour or Miyata 1000?

So many options...