Its the unsung smaller brother of you know what, and time to give it a bit of attention. I picked up a H for $700 a couple of years ago, purportedly 'going', with the idea of just racing a four stroke dunger in the heaven 250 4T class. The 'going' bit proved to be a euphemism really - unless you define going as the ability to roll on wheels, which it did.
Top end clapped out, rear shock no good, running gear - marginal.
Eighteen months later and its got a rebored cylinder, a YFM350 cam and (1mm oversize) valves, and a flow ported head. Tossed the oem carbie away and put in a TTR250 carb. Works Performance monoshock and IT175 forks.
Two years later and I've finally got the jetting sorted, and she runs a beaut. Vuury nice mid and top end, and crisp jetting all the way thru. New suspension all good too - pretty raceable unit methinks! Sad thing is, not sure I'll be the one racing it - putting a lot of time into racing dirt track these days, and don't do heaven events any more. She's good for a few things, but dirt track wouldn't be one of them. (doing up a '69 TS/TM250 for that).
I can vouch for there being some nice extra horses in these things if you go hunting for them - she pulls like a train!