Kirk, yes it sounds like you have the larger t/case that was fitted to the 3.5 V6. We didn't get the 3.0 V6 24 valve in the Paj here in Oz (only the 12 valve 3.0 V6 & 3.5 V6).
We only get the 24 valve version in the Challenger and Triton.
Attached is a pic of the larger t/case showing that the gears are all accessable from the front of the case. With the smaller cases you have to pull them apart totally.
The gears I sold directly to people with models I weren't sure about I always got them to check the part no's of their t/case gears with their local Mitsu dealer just to make sure. I guess Mark wasn't aware of this potential problem. I will be the only one selling these gears from now on to avoid problems such as yours.
Of course you can sell them to a forum member (I'm sure someone would be interested) or I can facilitate a refund from Mark. It's up to you.
I'm really sorry about this Kirk but to be honest I was afraid it would happen because 2 other people were selling these gears without having any Mitsu tech knowledge.
It maybe cold comfort for you but the same thing happened here as well. A guy bought his 3.5 V6 Paj to Marks 4wd Adaptors to have 2.85 gears fitted. It was only after the mechanic pulled the t/case apart did he realize they wouldn't fit. The mechanic wore the cost as he was a agent for Gearmaster gears and thought the 2.85's fitted all Pajero's. The owner was pretty pissed about it apparently. All he had to do was make one phone call.
Also we will have 3.15 gears available for the larger t/case very soon.