Based on several customs I've seen on the net.
My first one was a repaint of classics Silverstreak. This time I've hacked apart a Sideswipe and used a Jazz head.


Alt mode is unchanged, although as you can see I couldn't quite get the panels to line up.


I cut bits off the bottom of his legs so I could turn them around and give space for his feet. The bits that were cut off were glued to his roof so car mode is still seamless. You can see them behind his head in the below photos.
I also whacked on some G1 Overdrive reprolabels.




You can see here I overestimated how much space would be needed for his neck piece. His head is also a smidge too small for the head post on Sideswipe, but it's only when you're this close that it's noticeable.


And here he is with my original Overdrive custom and his base model Sideswipe.