Improving acceleration using 2bbl Carburetor?

A 64 Valiant is almost 60 years old. If you have one with an unknown history that does not run well, you need to check a bunch of things you probably wouldn't on a five, ten or even 20-30 year old car. So, in addition to the usual plugs, points, valve adjustment, etc., I would check the following:
1. Do the centrifugal and vacuum advance mechanisms in the distributor work?
2. Is the TDC mark on the harmonic balancer in the correct place? If not, you can't time the motor correctly.
3. Is the muffler clogged? I've seen 'em clogged so badly the motor would barely run. One el cheapo way to test is to hacksaw the exhaust pipe ahead of the muffler and run it w/o the muffler (not permanently, of course).
4. Does the heat riser valve work properly?
5. Do a compression test.
PS: an exhaust manifold leak is not a "vacuum" leak. (Intake leak, yes, exhaust leak, no. Bad vacuum hoses can also be a source of a vacuum leak.)
PS2: On the idle issue, especially when cold, have you adjusted the curb idle screw or the fast idle screw?