If I was in your situation I would run the 3 Port in the buggy and the 7 Port in the truggy.

For a buggy both the 3 and the 7 are great. I favour 7 Port myself. Run 1.1 springs and shoes of your choice on either of these in the buggy, maybe weaker springs on a loose dusty track, but the 7 definitly likes a later hook up so it can spool up, so 1.1 on the 7 always - IMO.

Truggy would suit the 7 Port. It has more than enough bottom for a truggy. Same 1.1 springs with alloy shoes.

The best truggy motor is the stock 5 port. Massive bottom end and great mid to top, with excellent economy. Run 2072 or 0801 pipe.

The 3 port is a nice motor, but would be more suitable for the buggy only.
It has a more linear power band and is smooth. 0801 or 2072 pipe.

The 7 Port has good bottom and incredible top end. Not quite as linear as the 3 Port. Best with 2047 pipe and 0801 header, (or any longer header with same measurements as the 0801). This set up gives a nice power band and great bottom end response. The 0801 or the 2072 pipes are also nice on the 7.
Of course all this is my opinion only. I am sure you will get some differing views, but 5 Port in truggy, 3 or 7 in buggy is a pretty well established set up for the GO engine range. We are talking stock motors here. Modded motors are a different thing all together, with the modded 5 Port being the best buggy motor of the lot (with the exception of the new and only just released MG66 I would expect) - once again IMO