Freeplay CM4

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Here's also another interesting option.
https://www.waveshare.com/product/raspbe...-board.htm
https://www.waveshare.com/wiki/CM4-to-CM3-Board

It seems like they do another sort of odd thing and route GPIO44/45 from the CM4 to where the CM3 would have GPIO28/29.  That's not great, except that the Freeplay CM3 routes those to R29 and R30 and then to GROUND.  This just gives a better spot to try to solder to (after removing the R29/R30). 

   

It's a thought.  I'm not sure if it's better than the route you're already going.

FYI, they also have this interesting Zero->CM3 adapter, too.
https://www.waveshare.com/product/raspbe...dapter.htm