Looking for drawing/plan - conversion of HO Mantua 4-6-0 into Sn3 SP# 17 (or was it #12?)

I've started to buy parts for a project of turning a HO Mantua 4-6-0 (loosely based on Sierra 3) into a Southern Pacific Narrow Gauge 4-6-0 based on an article I saw some years ago where this model was converted to Sn3. In the article the exact locomotive it was converted to was SPNG #17.

But now I cannot remember WHERE I saw the article. Andrew Brandon (a member on here) thought he remembered such an article too, but neither of us can remember where it was. So far as we can find it wasn't in the Gazette, was it in Model Railroad Craftsman or some other magazine?

There was an article in Model Railroader in the 1980s to convert this same model into the much smaller Southern Pacific Narrow Gauge 4-6-0 #12 though - so both of us are thinking we may have remembered this wrong - however I swear to God the article was newer, maybe 2000s.

So any of the SPNG experts help me out here because I've been going crazy trying to find this (maybe imaginary) article.