I don't think the 2 wheel kit will make a difference on track tension so:
Poo says: Put rear of sled on a stand. Measure forward from the center of the rear wheel 16". With a 10lb weight hanging from the track the distance from your hifax to the track should be 5/8". If I remeber right this is for all track lengths.
I myself adjust the track so it has at least 5/8" if not more in about the same spot 16" forward with no weight. Then ride it, if it ratchets tighten it up. Find that fine line just before it slips. And of course if you are running extrovert drivers you can run it much looser.