Dave, I can't comment on the electrical to gas, but I have learned a little on the process for converting the YM-15 I bought from natural gas to propane. I thought I'd find someone out there who had done this, but I was surprised to find very little information online regarding roasters (lots of info on converting stoves, dryers, etc).
In general, what I've learned about the Ambex YM-15 burner and jets is that the flame distance from the drum, the jet distribution pattern, and flame shape are important in distributing heat evenly across the drum (the jets are actually "slotted cap jets") so I can only speculate that the distance of an electrical source from the drum would be different. I think there could be a correlation between the stirring vanes in the drum and the pattern of the jets but I haven't mapped that out yet...
So far, all I've had to modify is the Robertshaw gas valve and replace all 15 slotted cap jets (be sure to blow out the line from the valve to the burner). The aperture in the NG parts are larger than those in the LP - LP is under pressure. I'm documenting the process, as well as the parts suppliers, description, and part numbers. I'll post it online so others can benefit from my experience.
I'm really looking forward to the Roaster Maintenance class that Don @ Ambex will do at the SCAA '09 conference, where one takes apart a YM-15 and puts it back together again. I'm slowly documenting each part and looking for a parts supplier in the event that I need to do maintenance. I really want an exploded BOM for this roaster, but again, I haven't found one online yet.
So, I'd be interested to know if it's possible to convert from electric to gas, without breaking out a hack-saw or torch, and replacing major parts. Something I'm really interested in, is wood-fired coffee roasters - I've got the bug real bad... I sit on 33 acres and have access to another 50 acres with tons (really) of hardwood that is renewable and not subject to price swings like gas (just ax swings). If I harvested those trees that have died naturally, I could roast non-stop.
Woody