Heres what I have done. I have retained the stock fuel pump on my FC, ran it to a T line which is connected to my holley 4-7psi regulator to a weber dcoe.

Heres a makeshift diagram...


[45DCOE]======[pres. gauge]=[fuel pres. reg]
.................................................. ...............I I
.................................................. ...............I I
..............................Fuel Feed from EFI> =[ ] ... (A Brass T setup to feed regulator)
.................................................. ...............I I........ (and return)
.................................................. ...............IxI <--- Hose clamp to crimp line
.................................................. ..........Fuel Rtn.

Will this be sufficient?

 

Maybe I'm missing something from your post, but you definitely need a regulator made for fuel injection. A regulator that can regulate from 4-7 PSI is made for a carb setup. Here is a link to a fuel setup that works.
Reted's parallel fuel rail setup

 

Is this a carb conversion?

 

Yeah.

I can't find a malpassi so I picked up a holley and plumbed a T on the feed side and crimped the return line.

 

Do you guys think it will work?