The subject of the 700 R4 and it's "problem" with it's very low 1st
gear causing it to SLAM into second gear has come up frequently so I
though I would post the solution. An adapter from TCI part #376710
corrects the placement of the TV cable to an Edelbrock carb. It
provides the proper geometry ( and you thought you would never use it
when you were in high school ) and cable pull for both the 700R4 and
the 200R4.

I spent many hours trying to get it right on my own and came very
close. This adapter instantly gave me a perfect shift. The 700 does
not slam into gear when this cable is set up properly. The application
on an Avanti is a little tricky because of manifold clearance and some
grinding is involved. If you have an Edelbrock on an Avanti you've
probably trimmed the linkage and the piece that's trimmed is a locating
point for the adapter. I would be happy to send a tracing of intact
linkage so you can place the adapter in the right position.

Here is a link to pictures

R2 R5388