If you are using a carby then no need for the speed sensor unless you want to try and fit VN-VP cruise.

TH400 cable attaches to the passenger side of the box, and the cable is routed through the middle of the firewall to avoid small radius bends. Just look at a HQ-WB parts catalogue for how TH400 or TH350 cable is routed and supported.
HZ or WB will also show you how TH350 kickdown works off a carby so you can deal with the 4L60 kickdown.

What are you using for torque converter control? A B&M kit?