Hi Paulie, what a nice problem to have. All these GO motors available and we can't decide for you

Looks like it's come down to the EBMods5 or the Massive Mods 3 Port R Spec.

You say you are new to nitro buggy. I am thinking the EB5 might be too much engine if your new to nitro, especially if your track is dusty and loose as you have stated earlier. I run a MMods Stage 5 5 port in my buggy and it can be a handful, even with 6.5 mm restrictor. Great on a sticky track, but you need to be real easy on the throttle if it's loose. The modded 5 Ports do have a LOT of power for a buggy.
On the plus side, it does come run in and ready to race.

The 3 Port R Spec I feel would be better suited to your conditions. They are a very linear motor and very easy to drive. Fitted with an 0801 pipe (which you can get as a combo kit with restrictors) this motor would be plenty powerful enough for your tight track, especially if you got MMods to do a Stage 3 sleeve mod before they shipped it out to you You would need to do this anyway, as you can't sell stock GO motors internationally.
As far as break in goes, the 3 Port Race motors are nowhere near as tight as the 5 and 7 ports. Once you have a few tanks through you will find it doesn't jam on the starter box much.

Just to add to the confusuion IMO the 7 Port is the ultimate buggy motor. They do have awesome top end, but they are not that far off the 5 port for bottom end when run with the right pipe and clutch. The bottom end is still there, it is just comes in a bit smoother than the 5 Port, which suits a buggy perfectly. Short tight track run the 0801 pipe - sweet. Longer track run the 2047 pipe with the 0801 header - perfect. Down side for you is you would need a heat gun etc to break this motor in.

So IMO your best option would be to go with a Stage 3 3 Port R Spec and 0801 Pipe.