So what is the difference other than the F and R markings? I have a good Front housing, but need to replace a rear housing. Can I simply use a front housing in the rear?

 

if you don't need EGR then it doesn't matter what location housing you use where. the only difference between F and R is the direction that the exhaust port air holes are drilled in the housings towards the exhaust sleeve.

 

Great, got rid of that stuff long time ago.