I had a lot of trouble removing my Shift shaft bushing from my Mercury 70hp lower unit without this tool. I ended up having to angle grind a bit of round tubing and get it off that way and it wasn't very pretty.
The tool costs around $23 USD and is being sold as "18-9817 - Bushing Tool, 91-31107Tl".
Being in Australia it would end up costing a fair amount with shipping and now that I have a printer I decided to make one.
I thought that maybe someone else might be in my position so I'm uploading it here.
I printed mine at 0.15mm and it fits my bushing really well and an 18mm spanner fits snug on the top.
Hope this can help someone! ..and their wallets. :)
So I printed @0.15mm with 20% infill and 6 wall line counts and it feels strong in hand, I haven't tried wrenching the bushing into place to see if it give out or not but it feels really sturdy.