Since I got the truck I’ve been trying to figure out a replacement mechanical fuel pump. Previously I mentioned one of the possibilities, which was to get a newer fuel pump for a more common L-series Datsun engine and modify it to fit the E-series engine.
Here is a picture of the original, OEM fuel pump that came on the E-1 engines, complete with tin-man styling and a cool priming lever (picture originally posted on Ratsun by Steve).
And here is a shot of the Nikki fuel pump that was on my truck when I got it. I am fairly certain this is a J-series engine fuel pump such as those found on the engines of the 520 and 521 trucks that followed the 320 in the Datsun line-up beginning in late 1965. Note the angle and length of the fuel pump arm are similar to the original E-series pump above.
I found and bought an L-series fuel pump. This is the pump that was found on 510s, 240zs, and 610 and later Datsun trucks, so they tend to be more readily available than either the E-series or J-series pumps. As shown below, the mounting surface and bolt-hole spacing between the J- and L-series pumps are identical, which is promising.
But clearly the arms are different in size and angle (L-series pump left, J-series right).
And the L-series pump is a Kyosan Denki whereas the J-series is a Nikki.
The fuel pump arms are mounted into the body by a pin. I was unsuccessful trying to press out the pin on either of the pumps, so I will need to take this to a machine shop to see if they have any luck swapping the arm from my E-1 compatible J13 pump onto the brand new L-series fuel pump.