OK, Here's the scoop
Talked to Mike at Powersource Canada, and yes there is a bulletin about a cold weather kit available for this engine. Mike was saying this is the same engine as is used on the home standby generator, which also have icing problems. The instructions in kit # 6174 describe installing a different heat shield over the muffler, removing the rain cap off the Donaldson air cleaner, attaching a hose to the raw air inlet, securing with clamp and rotating the end of the air cleaner housing so the raw air is pulled from around the muffler through the hole in the new muffler heat shield.
Seek and ye shall find, thanks Roy for your help on this one. I'll check with my customer on the weekend and probably order the parts right after Christmas, then hopefully report back to the forum with the results once we've had another cold snap. All the best,
Sky