Before you all go drilling holes through Heljan chassis...
Frateschi produce an A1A-A1A model of EMD's G12 export design, which although marketed as being a HO scale model is actually more likely to be OO. Here's a photo of the G12 body (Bo-Bo chassis version) compared to a 1:76 drawing:
(Photo courtesy of Donal Murray)
I chatted with Glenderg, who sourced a drawing of an A1A-A1A G12 and scaled it to OO. Look how it compares to the Sulzer:
The Frateschi locos can be bought online for around €80 including shipping. For example: http://www.ebay.ie/itm/HO-1-87-FRATESCHI-Locomotive-G-12-A1A-RFFSA-/272005336703?hash=item3f54c80e7f:g:KrcAAOSwDN1UPoo c
Judging by this YouTube video, it's not a bad runner, either:
I'm not sure if it's DCC ready, though, but for that price and the problem it would solve, hardwiring may be worth the effort. I have seen DCC'ed version on YouTube..
Edit: Testimonial from a friend who recently acquired a Bo-Bo version...