At the back of the P, there should be a couple of cylinders tucked under the bunker. Casting are supplied for these but I've hit a problem.
A OO guage chassis is quite a bit narrower than scale. The two cyclinders are scale width. Something has to give. Either they breathing in a lot or one of them goes in the spares box.
Sadly, the long horizontal cyclinder will be left for the P4 modellers. It's width is about the same as my chassis narrowness. I don't think anyone will notice.