I’m knocking around the idea of modifying an old brass CP decapod into a CPR 0-6-6-0. Any feedback? It should be somewhat straightforward with all the good 6 coupled mechanisms out there…
Ideas???
I’m not an expert, but I do believe you’re on the right track. For others reading this, CP’s 0-6-6-0s were converted into Decapods. Unfortunately, I have no experience modifying steamers, so all I can do is congratulate you when you’re done 
Should be an interesting looking engine, with the front cylinders and front driver set facing rearwards, face to face with the rear cylinders and rear driver set, plus the large box structure and heavy piping between the front sand dome and the steam dome and the large air cylinders tucked under the chin of the smoke box…
You may already have the following info, but here it is in case not. 
The first five engines (1950 -1954) were built as compounds (Mallets) while the last (1955) was built as simple (see cylinder sizes below). The engines were renumbered 5750 to 5755 and converted to 2-10-0 Decapods, with 23.5" x 32" cylinders but keeping their 58" drivers.
Pages 152 and 153 of Omer Lavallées “Canadian Pacific Steam Locomotives” have several photos of 0-6-6-0’s, also of 5755 after conversion. Page 7 of BRNMA’s “Canadian Pacific’s Big Hill - A Hundred Years of Operation” shows No.1950 at Field around 1909/1912.
Class R1A No. 1950, cylinders 23.25" and 34" x 26"
Class R1B No.'s 1951 - 1954, cylinders 24" and 34" x 26"
Class R1C No. 1955, cylinders 20" x 26"
Yup, I’ve got most of that info, and I’m in the process of checking specs on some of the newer 6 coupled mechanisms. My first concern was with driver rotation after turning the one set around, but then I grew a brain…
Then the idea of chopping up a brass decapod gave me pause for about 5 seconds.
I look forward to posting pics of the completed model, and I hope it pulls as well as the prototype did.
An interesting read on the CPR 0-6-6-0’s and the later converted decopods.
http://www.trainweb.org/oldtimetrains/photos/cpr_steam/decapod.htm
I remember someone stating in one of the model railroad forums that there never were any mallets in Canada.
When someone corrected the individual about the 6 CPR locomotives they responded that they did know about them but as there were only 6 that they were not worth noting.
That train site confirmed I was not crazy seeing a 5700 in Moose Jaw back in the 1950’s and I believe it was used as a switcher, I never even knew what it was, thank goodness for cameras, and to think they started out as a mallet, and I was looking at the largest switcher in Canada.