I have had several 460 powered trucks and vans + a couple of Lincolns and did a lot of tune up --upgrade type work n friends cars/trucks--

Ford retarded the camshafts in the mid 70s 8 degrees at the crank and lost 40 ft lbs of torque---I had some lower gears made by Cloyes with 7 keyways so I could set the cam/crank timing anyplace I wanted---you can just use a early lower gear but check to see that the keyway is EXACTLY in line with the adjacient tooth---the retarded sets are visably off set--a good place is to even advance it 4 degrees more--

On the ignition timing----you probably aren't getting enough early lead and might be from the vacume advance being on the wrong vacume tap to carb/manifold as those smog years hade dozens of different valves/temp control thingies to made the exhaust pipe smell right---

A good test---advance the dist several degrees (30 to 35) and then just jump on it from an idle---if it wants to run good, you need to do some dist curve work and maybe the cam is ok--if it is still lazy---pull the front cover and redo the cam timing

You can run the engine without the front cover to see if it seems better before you have to button it up--just crack the throttle and see how it revs---