Ok there have been a few posts asking about this lately. If you don't use the proper bracket for the Mopar, and just the universal one that comes on the carb, you may not be able to get the secondaries fully open...
First you need to get the holley throttle bracket for the Mopars, Holley part # 20-7.
Holley 20-7 Carburetor Throttle Lever Extension - Holley Performance Products
Here are some links to it at Summit Racing and Mancini Racing:
Holley Throttle Lever Extension
After you get that bracket, then you need to install it to the carb. Here's how it goes:
Here's what comes in the kit:
You will need to take the old stud off the original carb from your car..
It mounts on the bracket like this. But wait to install it until you bolt it to the carb so the stud doesn't get in the way of you putting the bracket on the carb.
Here's how the bracket mounts onto the carb with the two bolts and nuts supplied in the kit.
Here it is from another angle:
Here it is with the stud attached:
Here it is from the front. You may need to rotate the head of the top bolt to install the throttle cable ferrule as sometimes the edges on the corner may get in the way. You can see it's pretty tight in this picture. Try to get the flat side of the nut right near the stud, not a corner.
Here's another shot from the front and side:
Here it is from the back:
Here it is hooked up on an engine.
I like to put washers on each side of the kick down linkage to keep it in the proper position with a cotter pin on the end as shown here. The spring for the kickdown linkage also goes inside the outer washer just inside the cotter pin:
Here you can see the spring for the kick down on the right. Notice that the throttle return spring goes inside the fitting from the throttle cable.
If you are converting a 2 bbl engine to a 4 bbl, you will want to get the stock 340 4 bbl throttle bracket. Here's the link for it at Mancini:
Mancini Racing Throttle Cable Mounting Bracket
You can then use all of the stock 2 bbl kick down linkage, but you will have to lengthen the rod with the slot that goes to the carb. The center rod and the rod from the trans to the pivot bracket just behind the starter stay the same...
Here's a diagram showing the stock 318 2 bbl kick down with the ball crank linkage from the 67 - 72 vintage. This is from page 21-50 of the 68 Plymouth service manual available for download here:
MyMopar - Mopar Forums & Information - Service Manuals
Here are the throttle brackets compared side by side. The blue one is from a 318 2 bbl, and the black one is a 340 4 bbl style like the one in the link in the post #2 above. I have the mounting holes lined up on them so you can see that the 4 bbl one sticks out about 1 1/2" - 2" more forward than the 2 bbl bracket mount for the throttle cable.
Here you can see the mounting for the cable ferrule for the 2 bbl is horizontal and rearward, where the 4 bbl mount is more forward and vertical. This is the view looking from the top, so it's upside down.
With the 4 bbl bracket, you can still use the 2 bbl throttle cable.
But the rear mount for the kick down rod to the carb is in the same position relative to the engine on both, so you will have to lengthen the rod with the slot about 1 1/2" - 2". This is just as easy as making an extension to put on the end of the male threaded part. They do sell them pre-made now, but in the old days we had to make one ourselves...
First you need to get some round or hex stock and drill and tap it for 3/8" fine thread or 3/8" x 24 thread. Then get some 3/8" x 24 threaded rod and cut off a piece to put in the round stock that you drilled and tapped. You want to make the 'base' about 2" long and thread the threaded rod in about half-way and leave the other half of the threads to screw it onto the tip of the kick down rod.
Here's a phantom view of the piece of round or hex stock that you need to drill and tap to 3/8" x 24 thread:
Here is a shaded view of it:
Now you will need to cut about a 2 1/2" - 3" length of the 3/8" x 24 thread rod.
Then you screw the threaded rod halfway in the round or hex stock, then mount on the end of the kick down rod...
Here's some pictures of one I made many years ago and used on my daily driver - pardon the rust/patina... I also used a jam nut on each end to keep it from walking after it is adjusted..
Here are the diagrams and instructions from the 68 Plymouth service manual on how to adjust the 67-72 style 3 piece kick down with the ball crank.
Here's the diagram:
Here's the the instructions on how to properly adjust it. If the kick down is not adjusted properly, the trans won't down shift properly and the line pressures won't be correct and can lead to early failure of the trans, so it's important to have it properly adjusted.
Here's how it will look when done and all hooked up properly. This rod was the proper length and didn't need to be modified. Good luck all, happy motoring and I hope this helped you...