I know this is the race section, but....

I have 1979 D-100 truck with a 360. Cruises at 18-20 inches of
vaccuum on the freeway at about 2800RPM at 65mph, level road.
Motor is very mild and fairly new, in good shape. Nice truck.

But, I'm only getting 9-10 MPG. At that manifold vaccuum, you
would think there's not a lot of parasitic drag, binding, etc.
Also, coolant temp is stable and not out of hand.

The timing marks on the dampener are very hard to read, and,
I do not know for SURE if the TDC mark is really at piston TDC.
I realize I do need to nail this down...

I can't get a handle on the ignition timing. It has an MSD-6A
and some kind of Mopar distributor with vaccuum advance.
I'm wondering if I should buy a second distributor and have
a shop set up a specific advance curve, vaccuum + centrifugal,
something known at least.

If I buy another distributor, what's a good quality one ?
Maybe the MSD #8388 ? Another Mopar piece ?

I know I should look at the carb too (625 Edelbrock), but it
is in good shape and not weirdly jetted or anything. Really
there are no odd drivability issues.