Blown '69: TH-350 passing gear mystery

[Sleeper]

Hi folks, I have a '69 3/4 ton GMC pickup 2WD, 350. Three years ago I had a Mr. Goodwrench 350, small Weiand blower, and Holley 750 electric choke carb put in it. When I picked it up, the mechanic said, "the passing gear is not working--but it's so powerful you practically don't need it". That was fine, because it was a long process to get it to that point.

Right now, three years later, I'm getting the TH-350 rebuilt (at another shop!). I would like for my passing gear to finally work. The questions I have are:

1) Do I have a detent cable (or TV cable)?
(I have a Haines manual and it seems to indicate for early models that it has a detent cable--can any one clear that up?)Whatever it is, I think it's dormant.

2) Next, I suspect that the mechanic who did the original work may have gotten flustered during the switchover from the Rochester 750 4bbl to the new Holley 750, and perhaps didn't have the mindset or the patience to get a newer detent or TV cable [with the extra length that is possibly required for the blower setup?], so he gave up.

I want to do this right, so does anybody out there know about these TV/detent cables, and whether I need to order an extra-long/blower-model cable/or standard--if that is the case. Finally, If I do order it, will it connect right to the Holley or do I need some adaptors?
-I'm trying to do this sleuthing over the internet, so I can order a quik-ship part/s and bring it down to the shop in the next 5 days--without going down there and poking my head all through my vehicle during their workday.

Much obliged,
Sleeper