Gas Mileage???

brasil said
The pistons are Flat Top ( bought a endoscope to look inside the cylinders)

You may be able to see the markings on the flat tops, for TRWs I have the overbore size is marked on the tops.

The compression test showed 180-190 psi on all cyl.

How many bumps? Regardless, that seems healthy and also suggests cam closer to stock.

Vacuum @ idle with 16 deg initial is 15inches ROCK SOLID when I shift into DRIVE the vacumm goes down.... flucktrating very fast between 10 and 13 inches..

This suggests the fuel/air and timing are are not providing quite enough power to idle smooth in Drive. Try a little bit more fuel at idle (idle mix screws another 1/16 to 1/8 turn richer).

Sadly I don´t know...what kind of cam is installed... also the CR is unknown.

If you have the time and patience, you could measure the cam lift and and degrees each opens using a degree wheel and dial indicator at the rockers....

Intresting thing.... I found out that the engine makes a lot more power ...if the curve is slower.... with a fast curve the engine sounds very stressed! Using the slow curve ( curve A or Curve B from the MSD Instructions ) the engine pulls like a
TRUCK... Using a fast curve makes the "pinging / rattling " issue worse.

Don't worry about 'fast' or 'slow'. An engine engine with an efficient burn will need less timing.
What do those curves look like?
With an MSD distributor you may need to make adjustments beyond what they supply. Besides changing springs, you can make your own bushings or modify the shape of the curve. See link to forum I posted previously to find info on how to do that. But first you need to know what you have. Measure and plot it out from 500 rpm (or as low as it will go) to 4000 rpm (if you can do so safely).