cheap/easy mpg boosters?

look at raising the initial timing as high as you can get it and still be able to start it when fully warmed up.

On the exhaust pipe diameter, bigger is not always better, so consult a professional exhaust/header fabricator when it comes to appropriate diameter, cause yes restrictive pipes hurt flow=hp/mpg but a necessary diameter is needed to keep thing moving fast out of the engine-velocity.
oh and no exhaust leaks! lol

Multi spark, like MSD as menetioned, will help out a lot 2-3 mpg 'guesstimate'

Aired up tires to the max rating when COLD, they expand when hot and will fool you into thinking they filled enough.

Smallest fan diameter you can use and still cool efficiently as well as good belt/pulley alignment.

valve lash on the looser side may help sum.

A tight convertor, or a lock up trans would be very nice and an easy bolt in for a 'driver' or mild build.

GOOD ALIGNMENT too.