I just saw your post. I believe the chassis is all the same. Just different motors. The 125 and 155 use the same bottom end but a different bore on the cylinder. the 90cc motor is a completely different motor. So keep this in mind when upgrading to larger bore motor in the future. Good Luck! Changing to Elka shocks will also help the handling and the ATV FourPlay suspension is the best way to go if ypur going to MX it.
Adam McGee Racing 11 running 2 Pitster Pro's and a Xtreme custom flat tracker. Thanks Firepower Minis, Tbolt Usa, Atv Fourplay, Pitster Pro BRM Offroad graphics, Titain Motorworks , Motocross Vests Champions Choice
Moto X Outcast 2012 90cc 3rd place
Steve Nace Indoor Winter Nationals St and TT 2011-2012 and 2012-2013 2nd place.