Ive looked at doing this too. I have a 20' 155 khaos I put ice age rails on and an epic 2.8 track and pro gears. Trying to decide keep it for next year or sell and get a new one. I really want the QD2, series 8 165 track on a 155 tunnel. IMO the easiest least expensive way is to buy a 165 sled and cut the tunnel. I have yet to find pricing on the series 8 track, but my guess in the $1500 range retail price.
Good guesstimate....I have the part number for the new 165 track and retail is 1449.00. But the big question.......when will it actually be available?!?!?! That's the gamble if a guy goes with the 155 and upgrades to 165.