Cable vss to electronic?

[Jesus5150]

I have a 73 BOP Th400 that I'm trying to hook up to a glowshift 3 1/4 inch aftermarket speedo. I need to change the cable to a single signal wire and have spent 2 days trying to figure out how. Some say swap the gear which sounds like a load of Crap. While others say get an inline pulse generator. While this sounds like the correct way to go, do I need a 2k? 4k? 8k? 128k?

Had I known it would be this big of an issue I'd have kept stock, dim, jumpy gauges.....

Also, where is the easiest place to get a transmission temp probe fitted? (1/4npt)