Technical 1950 shoebox speedometer issue

Ok,, I bought a shoebox with a chevy 350 already installed..The person told me it had a TH400 tranny..no problem..i am in the process of rewiring it...I jacked up the drivers side to measure for a new speedo cable going to my stock speedo and,, no input..Looking closer all I can see is a Plug where the speedo cable should go!! looking closer and searching online it appears I have a 700r4 tranny! Now...how can I adapt (if possible)my stock mechanical speedo to this Plug thingy on the tranny??? if at all

 

Answer will depend on which tranny you really have. If you are not sure, you can tell by the tranny pan. You should be able to find comparative diagrams of the pans on HAMB or google it.

 

pretty sure its a 700r4..theres also 2 wires in a connector by the shifter linkage which im assuming is for the lock up mechanism.