Thats what I'm currently in the middle of with my GP38-3, removing all signs of the GP50 turbos. You seem to have 2 choices for the exhaust hatch, there's a Atlas spares part but that doesnt have a plate bottom, like the other option which is a Cannon part. I need the Atlas one as I dont need the plate, but a lot of the 38-2s did have plates.
Thanks for those photos Tony, they'll help a little with my NS 38-3, if by any chance your ever out fanning and get a chance for a few roof shots of a NS 38-3, I'm still trying to figure out if the removed middle fan is plated over with a round piece or a rectangular/square plate of metal, personally I'm of the opinion that its the latter, I've zoomed in on as many photos as I can find but things get too blurred to be 100% about it.
Dave