Finding Mercury model number

[BluesLover]

I hope I'm now posting in the right place and that someone can help, I've run into this twice now.
Not able to find a tag with the model number, but there is a tag with just the serial number, located on the mounting bracket.
One instance is on a 1991 XR4 150 (serial 0D038324.
Second instance is Serial #0(6orG)167561, 2.5 Litre XRi
I'm trying to determine the shaft length before I buy it, i need a 25" shaft.
Unfortunately the seller hasn't been able to take a reliable measurement from the boat or motor, and it's not close by.
Any one know of another location for the model number or a way to get it from the serial number?
Appreciate any help, thanks in advance

[JOE54]

neither are 25 in mtrs , both are 20in , never has been 25in xr4

[leonreno]

Also easy to know usually by what boat it comes off, if off a bass boat it’s almost always a 20”.

[BluesLover]

Thank you for the responses leonreno and Joe54.

[JOE54]