Fuel tank differences

[WFarm]

I’m considering swapping my 31 gallon tank in my 75 Blazer with a 31 gallon baffled tank from a 87 Blazer and was trying to determine what differences there are between the 2 tanks. Have read numerous discussions but none really have answers. Seems the opening for the pump is a bit larger on the 87 (makes sense as the 75 only had a sending unit) and the filler necks are different sizes?

 

[bucket]

Sender opening is the same size. I don't remember on the filler size... I can't remember if it changed like the trucks did.