Two years ago, when I started looking for a pre60 bike, I picked out a couple of options - Greeves Hawkstone, or a 350 MAC Velo. My reasoning was
1/ the Greeves was a made for racing steed with no shortage of reasonably priced parts. It was light and easy handling, which suited my lack of fitness level. The disadvantages were a power level well down on a 4stroke of that period. So gearing must be spot on to suit different tracks. However, less tiring in long races.
2/ the Velo seemed to be a good inbetween 4stroke option. A bit lighter than the 500s, nice 54in wheelbase, many performance options, don't vibrate too much, good 4speed. I rode one on short circuit and speedway years ago with what seemed humungous(?) power on methanol.
Couldn't find either, ended up with the HJH. Go figure. No regrets.
One thing I learned by the time I finished, by the time you set up the rolling chassis with chains, sprockets, tyres, shocks, forks, etc etc, 2strokes are no cheaper than 4strokes to restore. And it sure helps to get as complete a bike as possible, evan if you plan some very ambitious alterations.
Would still like a MAC, though.