RECENTLY PURCHASED A 1974 RANGER F100 WICH HAS A 390 IN IT I HAVE BEEN TOLD THAT THERE ARE TWO OUTLET SIZES FOR THIS MOTOR ON THE PASSENGER SIZE. COULD SOMEONE HELP ME DETERMINE WHAT SIZE I NEED?

There are 2 different RH (Passenger Side) manifolds for this application. This manifold fits models with the 2 inch outlet only. The other design has a 2.32 inch outlet (Casting #: C5TZ9430A).
THIS IS WHAT I FOUND ON A PART WEBSITE.
HERE IS THE SITE https://www.am-autoparts.com/product...?m=1522&y=1974

 

Welcome to FTE, lots of good, knowledgeable people here.
Your truck should have the 2" exhaust.
The Ford parts catalog doesn't show anything about the 2.32" exhaust and these trucks.
Just a note, casting numbers and part numbers aren't the same animal.
It shows the manifolds are:
Manifold, exhaust, RH
Fits: F100-350, M450-500 w/ 360-390
P/N D0TZ-9430-A

Manifold, exhaust, LH
Fits: 73-74 F100 w/ 360-390
P/N C5TZ-9431-A
or
Fits: 73-75 F10-350, M450-500 w 360-390
P/N C8TZ-9431-B
use with C1SZ-9448-E heat shield

 

Just wondering why ya can't measure your manifold and the exhaust tubing....