4000 rpm's at 60, no 3rd?

It doesn't matter if you have the old style or new style linkage as long as all the pieces are from a matched set and adjusted properly. There is no internal adjustment (except for the throttle valve idle adjustment and that isn't the problem) so there's no need to drop the pan and try. All the adjustment for the throttle pressure is done externally. It's quite possible the use of the non stock Edelbrock carb. in conjunction with stock type linkage is the problem. The ratio of how much the linkage is pushed back is more with an Edelbrock carb. cause it's mounted off center farther. Edelbrock sells an adapter to install that corrects the ratio and with it I don't think you will have to have that home made adapter to raise the throttle cable up. If that doesn't fix it someone has been inside the trans. and either cranked up the line pressure to try to make it shift harder or installed a shift kit that isn't very good causing it to hang in gear too long. I've seen that happen with some shift kits.