My car is 5/16 all the way through - put a Holley dual feed on today and using the supplied 3/8 hoses for now - best way to step - up from 5/16 - 3/8 between pump and carb ? I was hoping for a barbed adapter at Advance or Home Depot. Pump has 5/16 , short hard line on outlet side that does a short "U" (340). Is stock pump enough PSI for a 670 Avenger ?

stock pump should be fine (without knowing anything else about your build) and 3/8 from pump to carb is good.

If you lube up the hose you can slip a 5/16 hose over
a 3/8" radius fitting(this has a radius instead of
the sharp barb) its tight and a bit hard to get it
on but you can do it... the 5/16 and the stock pump
should be fine unless you really rev the heck out of
it... a larger supply line is much easier on the pump...
remember that pumps dont really suck, they create a
negative pressure and atmospheric pressure pushes
the fuel in to the negative

Thanks , that's actually what I did - (5/16 over 3/8 barb) it'll get me by for now. Originally boght a dual feed steel line and didn't realize where it terminated on a small block factory A/C car ...... deadheads right into the back of the compressor !