The starter I bought for my 107 was much smaller than the original. Still bolted up fine.
The reman starter came with a set of new crimp on terminals, presumably matching studs on solenoid, but they were not needed.

You need to get the right wires going to the right places. Get the wiring diagram if you can. This link explains what the 15, 30, 50 mean.

Bosch Terminal Designations

Wiring for starter can be found on page 106 here: https://www.dropbox.com/s/66n4ragz2in5ykk/126from86.pdf?dl=1

Looks like only terminals 30 and 50 are used? Thinner violet/white wire to terminal 50. Heavy black and slightly smaller Red to terminal 30? Double check this for your car!

Page 106/1 shows a different starter from 1991 cars it seems. With just one wire from battery, seems like that is what the link in your original post may have had.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5