Looking for direct start conversion for my D7 3T. These were built by Auto-Sec of Sherman TX.
On the ACMOC site there is a sticky on the top of the discussion forum that is all about direct electric start conversions. What starters, details for drilling the hole, what drive you need, etc. Old Magnet whom is also on this forum is the expert on the conversions. He has posted the pertinent information on that post.
The 3T conversion is somewhat unique. There isn't any commercially available adapter so requires a fabricated adapter plate. I believe General Gear in Idaho or Auto-lec (Texas I think) make up conversion kits.