bnickel said:
the best way is to use a guage, but you can get it close by adjusting it so that there is just a slight amount of slack where the cable attaches to the throttle body, and i mean slight amount of slack, less than 1/8", but even then i would take it to a tranny shop and have it adjusted correctly with a guage, or just call one and ask their advice
I will be the other guy

I didn't use a gauge at all.
This was (more or less) my process, which my trans builder told me about. And yes, I was scared too of frying stuff - but just be patient and all will work out..
First, I removed the pump shot cams from the carb and hooked up the linkage, this way I can ensure I have the full range of operation. With the throttle closed, I had a slight amount of pressure on the cable - I set this by pinching the cable and pulling just a little bit - enough where I felt some spring pressure, and set it.
(put pump shot cams back on)
Very imporant - before you try ANY test driving, you want to make sure all circuits get filled up with trans fluid.. After the car is running for awhile, put it in reverse, neutral, all the gear - leaving it in each gear for a minute - and repeat this process for the gears a few times.
If the gears feel like they are engaging the way they should (not stalling shifting into gear), then you should be ready for a limited test drive. Drive in reverse a bit, then put it in 1st and drive around some.. If all is still well, you graduated to 2nd gear.. Be nice and easy from 1st to 2nd and pay attention to the shift point - the shift point is based on CAR SPEED, not rpm when setting this. If it shifts at the right speed, all other gears should be just fine - if the shifting is too late or too soon - stop the car right there, and readjust it.
I just noticed a small conflict - nickel think 1/8" of slack - I have my setup to be preloaded about 1/4". I didn't do it to be different, but IN MY CASE, the shift points were at the right speed, so I went with it.