The diagrams on page 1K 10L of the 1981 parts book explain a lot.
Early 1850s and Sprints were fitted with a 312167 fuel pump. This is commonly referred to as the "short arm pump". It was fitted with a single thin gasket.( But note that the workshop manual refers to adjusting the fuel pump pressure downwards if neccessary by fitting extra gaskets. )
Later 1850s and Sprints were fitted with a TKC3419 ( = RKC5051 ) fuel pump together with a 13mm plastice spacer block part number UKC 8523. This is referred to as the " long arm pump ". The spacer block moves the later pump furthur from the mating face on the cylinder block to give the same pump pressure.
They give the change point as "May 1978".
I've taken a sample of each pump and drawn round the operating-lever profile of each pump.
1 Is the early slant 4 pump, which is actually a QFP32 QH version
2 Is a later slant 4 pump, QFP33 QH or 17110029 for a genuine AC pump.
3 Is a later slant 4 pump, with the spacer block fitted.
A genuine A.C fuel pump for the early slant 4 cars has 7990047 stamped on the operating lever.
A genuine A.C fuel pump for the later 1850 / Sprint cars is stamped 7990487.
If swapping from early to late fuel pumps you have to change the fixing bolts as well.
Early (short ) are 149673 x2
Late ones (long) areSH605101 x2
In each case the mating face of the pump is on the LHS of the graph paper.
Try printing this out at various scale factors to get the 50.00mm scale I've drawn in at the top.
Now 1300s and 1500s are different again.
Early 1300/1500s have RKC1624 pumps
There is no mention of what later 1300s have but later 1500s have an RKC5049 pump ,.longer studs TE605041 and this UKC8523 spacer block. The profile of the 1500 pump lever is very different to the slant 4 item.
Slight problem is the spacer block is NLA so its going to be EBay or similar.
And yes I've got caught out with a so-called "genuine Sprint long arm fuel pump ". It is similar but not close enough and has a different number stamped on the operating lever.
HTH,
Tony.