Hey Neko! I've replaced the speed sensor on my Blast. It's super easy.
Personally, I would NOT want to mess around with trying to get that "universal" gauge unit to work with the Blast's wiring harness. The gauge may be universal, but I guarantee that it's going to be a massive pain in the butt to make work right (and - as 34:19 has mentioned - the Blast doesn't even support the majority of the "features" that this universal gauge is offering).
I'll agree with what Mike said: Just buy the speed sensor (available here:
https://st-paul-harley-davidson-buel...eed-sensor-l9c), chuck it in, and get back on the road.