can't get above 70 MPH?

[BradMph]

DO you have the right vacuum line connected to distributor so it advances correctly. Almost sounds like your distributor might not be advancing correctly. A good test is to remove the vacuum line at carb for distributor and remove distributor cap and rotor. Suck onto the hose end that removed from carb and make sure you see movement in the distributor. The advance vacuum mechanism in the dizzy should turn a bit at a reasonable vacuum as you test it.
If you have the stock air cleaner also, make sure there is a vacuum line going to the heat riser flap on top of air cleaner housing and that the flap inside the air cleaner is fully closed after being warmed up.
I had one experience with a car not getting to top speed and that was a 74 Toyota land cruiser. Though probably not your issue at all, but it's problem was a lack of oil being pumped to the head and we had to run a separate oil line to the rod tube. Very doubtful this is what is going on with yours.

Camoit asked if your getting full throttle also, the cables may be fine but is it open carb flaps completely and is choke fully open as well when warmed up.

[Kaos731]

DO you have the right vacuum line connected to distributor so it advances correctly. Almost sounds like your distributor might not be advancing correctly. A good test is to remove the vacuum line at carb for distributor and remove distributor cap and rotor. Suck onto the hose end that removed from carb and make sure you see movement in the distributor. The advance vacuum mechanism in the dizzy should turn a bit at a reasonable vacuum as you test it.
If you have the stock air cleaner also, make sure there is a vacuum line going to the heat riser flap on top of air cleaner housing and that the flap inside the air cleaner is fully closed after being warmed up.
I had one experience with a car not getting to top speed and that was a 74 Toyota land cruiser. Though probably not your issue at all, but it's problem was a lack of oil being pumped to the head and we had to run a separate oil line to the rod tube. Very doubtful this is what is going on with yours.

Camoit asked if your getting full throttle also, the cables may be fine but is it open carb flaps completely and is choke fully open as well when warmed up.

Hmm I guess I'll check the stock cleaner housing for that. And yes all the vacuum lines are going to where they are supposed to go. Now if it turns out to be the air cleaner, will an after market open air cleaner with K&N filter fix that issue. if I also use replace that hose with a K&N breather cap?