noob needs help with mileage - only 10 MPG!

First, thanks to all who responded with tips and suggestions.

I just got the car back from the shop and it is running much better.
Actually it ran well before, but it had idled rough since I got it. The idle is still a bit rough, but a lot better than before.

Here's what was done to it:

Pertronix electronic ignition installed
carburetor overhauled (it was missing the throttle return spring!)

the mechanic also ran a leak down test, here are the results:
cyl %
1 35%
2 30%
3 25%
4 25%
5 34%
6 25%

So I'm guessing (and hoping) that the electronic ignition and overhaul of the carburetor will improve mileage considerably.
I'll make another post once I refill the tank and can calculate the mileage.

What does the board think of those leak down percentages?
On a new engine they'd be terrible, but a 1980 engine with no telling how many miles are it on it, they don't seem that bad (or do they?).
Should I consider having this engine rebuilt? or looking for a rebuilt slant six to replace the one I have?