You will ran into this at times even with Briggs engines as replacements are install where we need to swap flywheel per instructions from Briggs where they sell an engine with a lightweight flywheel but the engine that being replaced requires a heavy flywheel. Actually there times that we even need swap out crankshafts but this where the tech doing needs to document those changes and make sure the owner gets this info in case they use another shop for repairs.
As for coming up with the part number all we can rely on is the info at hand and doing our best to research the equipment part lists. Yes the online IPLs can be wrong at times even the printed ones can be wrong. I have seen this several times lately with Briggs IPLs that other providers are not as careful in providing accurate info which gets us all in trouble.
It like the aftermarket brake calipers I ordered that were state as fitting an ATV I am working on but when they came in they were the right design but had the wrong fittings for the OEM brake lines. I am now in the process of rebuilding the OEM calipers. I will need to bleed the calipers through a more difficult method since the bleeders are frozen in place but as long as I get all the air out it doesn't matter.
