Old PS2 SW-9 Diesel vs New SW-9 engine cover/shell swap ?

I don't know for sure, but I would say with a high degree of certainty that swapping the shells should work.

MTH is extremely resistant to new tooling. The tooling is very expensive and they don't update the tools on most models. Same for Lionel.

I actually feel bad for newer people to the hobby that don't realize that the new model they thought they were buying could actually be built on 20 year old tooling with new electronics in some cases.

I would try contacting forum member GGG, his email is in his profile. He might possibly be able to repair your current PS2 version? Sure would be worth a try, IMO.

It'll be the same tooling. All of the SW models probably ride on the exact same frame, so you could even buy one from someone's existing stock and swap it right now, without waiting for delivery of new catalog items. 

Trainworld currently lists several SW9s on sale for $249. If you wait a few more days, I wouldnt be surprised if they ran a coupon code sale for presidents day, knocking off a few more bucks and you'd basically be at a wash vs. the upgrade kit.

Thanks for the responses I tried emailing MTH several times with no response from them on 3 different issues.

The direct replacement of the shell/cover really appeals to me but hate to make a 250 to 329 dollar mistake.