Has anyone tried a new carter mechanical pump on their 235?

There are two flavors I'm aware of from summit or rockauto:

Carter 2118
Carter 2999

I have the 2999 and cannot figure out a good way to thread onto it.
Both pumps are listed as 1/8-27 NPSF on rockauto... but I can't find any adapter that size. My fuel lines are 5/16 with 1/2-20 threads on their flare fittings.
Right now I'm using a 1/8npt to 1/2-20 flare adapter, but the 1/8npt doesn't seal without the aid of JB weld.

What thread sizes do you guys have on your fuel lines & pumps?

'59 Chevy Suburban, NAPCO