Slick 60's

Anyone have ideas on why adding a fuel pressure regulator will prevent the truck from running? After setting the rebuilt FE in the truck and initially getting it running without a regulator, i decided to add one. Then with the regulator installed it would only start if gas was squirted in the carb but then quickly die. After trying multiple settings on the regulator with no different results, i took it back out and it starts/runs fine.

I assumed its just a bad regulator with some type of blockage but I can blow through it with very little effort.....

Are you running a stock mechanical fuel pump?

Check if air can be blown thru regulator. It may be directional or incorporate a check valve. It also should be mounted in close proximity to carburetor when possible.
Paul

Shouldn't need a regulator with a stock pump
Or a aftermarket if it pumps 7psi or less

I'm not a fan of regulators... just another device to
Stick or clog up

Yeah I'd go back to running it without the regulator, I had the same problem years back with a 8BA, and a old stock car racer I knew at the local wreckers, said to get rid of the pump and regulator and put in a pump that pumped less than 4 PSI... problem solved. Sometimes we tend to try and out think these old Girls, doesn't work !

Mechanical fuel pump but not stock - i think rated at 8 or 9 psi out - that's the only reason I thought I might need a regulator (don't want to put to much pressure to the carburetor and cause problems there).

It has markings for in and out and it was installed based on those marking and right at the inlet to the carb. As noted in OP - I can blow through it very easily.

8 or 9 psi will likely overwhelm the stock carb; the original system operated in the 4- 5.5 range.
Non-return regulators can be problematic; it sounds as if yours may fit that category. That was my reason behind blowing a volume of air thru it; it may flow well at minimum inlet pressure, but block off sufficient flow at higher inlet pressure.

It's not a stock carb either - Holley. I guess i'm not sure if they(Holley) can handle higher inlet pressure without problems?

That is dependent upon the particular Holley. Check fuel pressure with and without the regulator with an accurate gauge; including "blipping" the throttle. If you don't see over seven psi, I'd toss the regulator.
Paul