Links to more oil pump pics and dims in the Sportsterpedia;
77-85 Oil Pump in the IH section of the Sportsterpedia.
86-Present Oil Pump in the Evo section of the Sportsterpedia.

With a 98 style gasket on the 79 pump, the gasket fits nice and snug as it should be.
There were 3 different fitting changes to the 77-81 pump but the body stayed the same.
A 1-1/2“ hole was cut into an aluminum plate with 4 holes tapped to mount the pump. ¹⁾

The 79, 98 and 07 pumps were bolted to and outlined on the aluminum sheet. ²⁾

The mounting surfaces are compared below.
The red circle indicates the projected oil entry hole in 77-90 engine cases.
The last pic is a projected lineal of 3/16” from the outside upper edge of the 98 style pump to the center of the entry hole in the case. ³⁾

You can see the change in gerotors and plates between the different year pumps.
98 and up oil pumps have a cam chest suction port built into the neck of the pump.
The drive gear on the shaft is the same from 77 to present. ⁴⁾

The gearshaft is longer on 77-90 oil pumps but the gearshaft to mounting surface heights are the same.
The body housings are longer on 77-90 pumps due to the clearances needed for the gearshaft, spring washer and separator plates (2). ⁵⁾

Scavenger gerotors got bigger through the progressive years. ⁶⁾

Feed gerotors got bigger also. The 07 feed gears were made thinner than the 06 gears but wider. ⁷⁾

The 79-85 pump was bolted to and outlined on the aluminum sheet.
The 86-80 pump was then bolted to the sheet clearly within the mark of the 79-85 pump.

Feed Gerotors:

Return (scavenge) gerotors: