have been gradually adjusting a bouchillion cable ,smallblock 727,b&m shift kit.
i now have it when the carbs wot the trans lever is fully back. when in Drive i get firm 1-2 shift and it does kick down firm when mashing the pedal. but i do get kind of harsh down shifts when slowing to a stop. i have been gradually moving the cable, a 1/8" or so. the previous adjustment in Drive the 1-2 was soft and kick down seemed late and didnt really feel the downshifts . is my current adjustment ok? or should i back it off a bit.

As long as it kicks down at WOT you're OK.

Adjusting so that the trans lever is fully back at WOT as everybody suggests often produces your symptoms. With correctly adjusted factory linkage the lever is not full back at WOT.

I have a Lokar cable in my 64 Belvedere that never worked correctly on the up shifts. As reported here. the Lokar set up is some what inferior when compared to the Bouchillon one.
I had originally set up my cable to make sure that I had the trans lever fully back at wot. The problem was that the trans lever was now not forward enough when at idle.
In order to get the correct geometry. I had to modified the factory trans lever by drilling and moving inboard the location of the cable mounting ball stud about 3/4".
I also added a lever return spring.

The downshift when slowing to a stop is because the lever isn't returning fully forward when you let off the gas, do you have the spring attached properly from the lever to the bellhousing that they provided? Also the whole adjustment according to their instructions is about a 1/4" total so I would go back to the instructions and make sure you have it setup as they say.
I put one in a few weeks back and it was perfect at the install. Also the lever should go all the way back at full throttle less a very small amount so your not bottoming the lever all the way back.
Ron

Hopefully a return spring like rarefish said, is all you need.

or

The problem with the cable kits is they assume everyone has the same throttle lever on their transmission. You may need more reaction on the transmission end which would be a shorter lever.

Presently you are only making a linear adjustments. You can adjust it forward or backward and find it is always a compromise on the other end.

The solution is a ratio change. The lever needs to be longer or shorter. Short is easy because you can just drill a new hole inboard, closer to the pivot.

Bouchillon set up gives you the proper lever also. Their kit is really plug and play.
Ron