The part number for you M17xR4 motherboard is on a long thin sticker attached to the plastic holder the RAM slots into, it's the RAM slot underneath the keyboard (Top) not under rear cover (Bottom)
Alienware M17xR4 Motherboard Part Number: THTXT or 0THTXT
Here's a link to a seller on ebay, I've purchased from these guys before with no issues
Close, I believe its 0FPV4P
I wonder what the differences are between the two SKUs. They look the same and they appear to have the same REV number.
Since I don't know the difference between the two SKUs, I would have to say go with what works and to match what you already have in your system already.
I think there may be even more than two, I've had a bit of a chat with Chris M and he has supplied a whole heap of different numbers again, which may be complete kits (Thermal past, cleaner etc).
If someone else could verify this it would be good, but I see no reason why the ebay listed part numbers should not work, they are listed as Alienware Aurora R4 motherboards, as long as the CPU socket is the same and the connections match everything should be fine, you could always ask the seller to take a few close up photo's so you can compare with your old mobo to make sure all the connection you need are there.
Do you happen to have the list of all the parts numbers for the R4?
I believe you are right as well since I did a photo compare between the two and besides some writing on chips and on the board, it appears the same.