What happens if you leave the kickdown lever disconnected on the Powerglide?
I know that if you do this on the Ford c4 or c6:
1. The trans will not kick down from "hi" (3rd) to "lo" (1st).
2. Even at full throttle, the shift points will be almost 1000rpm lower, eg it will upshift at 3900 instead of 4800.
3. It will not damage the trans, ie you can run a c6 for years this way.

Is the same true for the Pglide?
Reason is, I'd like to leave the lever off so that it upshifts lower at full throttle, just to see where it upshifts, before I hook the lever back up. I just added a 4v carb to replace the 250-1v Rochester so I am betting the Pglide will upshift higher, but not sure how much higher. I don't want to overreve the tired 250 finding out where it wants the 1-2 shift to be.

Don't.

If you leave the kickdown unhooked, the trans will shift at about 15-20 mph no matter what throttle you give it.
Very important on a Powerglide.

Another thing I have done in the past when linkage broke, is to wire the PG kickdown lever up to the MPH you want it to shift at.

I had a 66 chevy PU once with a PG in it. I put a 396 in it (back when I was young and stupid), -- no room for kick down linkage. It shifted into high at 10 MPH -- no matter what unless I manually shifted it into low. I drove it like this for several years so it would probably be OK.

Joe et al,
Thanks that is what I was after, especially about the 396.
Turns out I didn't leave the lever unhooked, I just set it up so it didn't quite kick down all the way.
That shifted about 4200rpm with the 250-4v.
When I made sure it would kick all the way down to the stop, it would shift at 4600rpm.

As noted, the part-throttle behavior is very sensitive to where the lever is set, and how much travel it is given. The Ford c4 and c6 kickdowns don't affect part-throttle behavior but the powerglide sure does. So, now I know.