Got my towing mirror upgrade / conversion started today - not a bolt on for earlier models but definitely doable. Here sre the short notes for those contemplating the conversion themselves:
Started installing the 2004 factory E450 mirrors from e-bay today. They are not direct fit, but with some drilling and plug splicing they install relatively easily. (Plugs are different, wire color and function is the same, one banana job on the wiring). Holes you have to drill are quite large, a tad over 3/4" (large unibit is your friend). Top & bottom holes line up perfectly, 2 center ones are the ones that need drilling. The cast stud pedestals on the new mirror bases are large diameter, the bottom center ends up being drilled & placed in the way of the brace for the inner door/window regulator support. I drilled the outer shell, removed the stud, and left it as is, allowing the 3 other bolt on points to hold the mirror to the body (just like the stock setup uses). As an alternative to drilling the 4th hole you could cutoff the cast stud pedestal from the new mirror base, but I had the drill out and not the cutoff wheel so I made the hole. The new positions require using the factory nut washer on the top 2 points, but Im swapping out the lower stud for a bolt to keep the profile lower because it locates behind the door panel. Its a 6mm x 1.0 thread pitch stud/nut on those pieces. Pics to come, and full write up on the swap. I like the look and functionality of the new mirrors vs. the old paddle style units, worth the swap.
I started with this:
Remove cap and screw at bottom corner of door panel
Remove switch cluster
Remove screw now exposed
Remove door handle recess panel
And remove the screw behind that panel
Now pull off the top black panel
A good tug gets it, and that exposes the last screw holding on the door panel. Once unscrewed, lift the door panel up and off the door