The main thing I'd do with any ST-70, new kit or vintage E-bay or yardsale find, is ditch the 7199 driver board and go with Shannon's ST-70 driver board. The quality appears to be the same as the original 1960s era Dynakits. A 1960s dollar had the purchasing power of $5 today, so the price is fairly good. (a kit ST70 in 1965 was $100, and a built amp was $140, approximately). The driver board was already assembled, it just had to be wired in, and tubes plugged in.
You'd save some $$$ by going the DIY route, it all depends on how much chassis drilling and punching and "finish" work you want to do.
The "middle" choice would be to get the transformers, chassis, and cap board from Triode Electronics, and the DIY driver board from Shannon, the board components from Mouser or other sources, and the tubes from any source of your choice. I've been recently getting my glass from "Eurotubes" and they have been good and fast. Hint: the new JJ KT-77s in place of EL34s are a nice low-cost upgrade.
HTH
/ed B in NH