I found a 1/4 to -6 AN for the mechanical fuel pump (see photo IMG_1017)at 

https://www.pegasusautoracing.com/productselection.asp?Product=3230

I'm surprised that the pump outlet is only 1/4-inch.

The fuel regulator (shown in photo IMG_1016) already has an NPT pipe stuck in its outlet so should I assume it is truly an NPT in and out or that someone made it fit?

What is a dead-head FP regulator? Yes, it's between the pump and the carbs.

The threaded holes are 1/8 BSPT (ID) and the pipe is 1/4 OD. 

Does seem rather paltry.  But let this be a lesson to you-all who think you need 3/8 feed and supply to feed lines with monster noisy 200 gal/hr pump to feed our massive 2.4l 150 HP engines. NOT. 

-4 fuel lines in the engine bay are just fine. -6 is massive overkill, but they look so darn purdy!

Thanks to all. Parts on ordered.

Deadhead regulator means no return line.

Good to know there are some AN/BSP adapters available.