Head angle, and length of rear end are as important as top tube length. You want at least 21″, the rest depends on what you are riding. If you want to go fast and jump bigger stuff (trails, less technical park) then slacker and longer. For street riding/flatland etc then 21″ TT, but consider with steeper head angle and short back end. Bottom bracket height is also a consideration, and a matter of personal preference – you’ll know from rolling around on the bike. I jumped off the BMX bandwagon when jeans got tight and bikes started getting short, steep and a bit crashy on the trails. Also … brakes. Do you want one? or two? Or none? That bike pictured above doesn’t have one. It also doesn’t have lugs for one, or cable stops. Can you fit them? HTH.
ETA – just seen you say bmx track, and it’s got a brake. Long low slack and fast could be best, with a big gear. Prob like what you had in ’88.