Hello DB,
Have done hillclimbing a few years ago with the NHCA on a relatively heavy TriBSA. A good bunch of chaps, and some challenging tracks.
The SRX always seemed to be a bike that was better than it was given credit for, kinda overlooked I guess as it didn't really fit in with any particular category.
Given you've got a tweaked motor, the TZ frame and big stoppers up front, it should be pretty light, be reasonably responsive, have quick steering and be able to haul up nice n quick too..... which adds up to exactly what you need in a hillclimber. Looks like a really interesting project.
Can't tell from the photos how good or how old the tyres are, but if funds allow, I'd suggest you get the best tyres you can afford, even if they're second-hand, bearing in mind you're looking at 60 seconds of maximum everything (with cold tyres) on tracks that range from smooth and dry to wet and bumpy and anything in between.
Just check out the lean angle the guys on the converted moto-crossers get!!!
Looks like you'll have fun