The Holley Throttle Lever Extension is only useful if you're going to use the original kickdown rod setup.
If you are going for the Lokar cables I would recommend you fab up something like Aspen500's picture in post #4.
My experience (with Lokar) is you should have the kickdown cable move the same distance as the throttle cable at any piont.
Therefore the geometrics is important, both cables must be attached the same distance from the carb linkage pivot point.
When I got that right and adjused the kickdown cable so it is at full travel at WOT, I was happy with the shiftpoints on my Aspen.
I made a 4 inch piece of slotted iron and bolted it to the carb in a 11 o'clock - 5 o'clock position. Then I attached the cables to it with about the same distance from the pivot point. Beacause the iron is slotted I can also adjust a little if I'm not satisfied.
I got no picture of my setup and the car is at winter storage now.
Kind of hard for me to explain in english so I made a schetch so you maybe see what I'm trying to say: