I've got a BBS 2-BBL on my 170 with the 3-speed push button tranny with the super six kickdown linkage. When I picked it up from the shop a couple of days ago, the mechanic had one of the brackets the wrong way, so the kickdown lever wasn't moving, and it shifted very soft and didn't stay in the lower gears at all. So I turned the brakcet the correct way, and then it held it in the lower gears too long and shifted quite hard. So I adjusted the kickdown lever, and the shift quality is softer and it holds the gears about the right amount.

My question is this - is it a problem to have it adjusted so that it holds the gears longer and shifts firmer? A part of me kind of wants that for better acceleration, but the rest of me doesn't want to have this tranny rebuilt or replaced.

Pretty sure you mean to say you've got a Carter BBD. The BBS is the 1bbl member of that carb family ("S" for "Single"), and the BBD is the 2bbl ("D" for "Double" or "Dual").
Good...sounds like you got it figured out. I've run into that same "upside down bracket" problem from techs who didn't understand how the linkage was supposed to go together.
Nope! The problem comes if you have it adjusted too short/soft, which is very hard on the transmission. You will not hurt the trans at all by adjusting for longer gear-hold/harder shifts. The limit is practical in nature: Don't adjust the linkage so long that the car never shifts out of 2nd when you've got it floored, or so long that the 3-2 kickdown occurs in the middle of accelerator travel. Other than that, you're fine.

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Too many people who were born on third base actually believe they've hit a triple.

Well that's good to hear. When I get the engine all broken in, I'll adjust the kickdown lever to hold the gears a bit longer to feel how much more power I really have.

Oh yes, I meant BBD - I probably read a post about a BBS carb before I submitted my post.