The MSR X5T kit at the hobbyshops right now is a standard MBX5 buggy with the MSR conversion. The buggy parts replaced by the MSR conversion are removed making it easier and cheaper to build a MSR X5T without having to buy both seperate and selling the un-used buggy parts.
The long arm truggy is not due until later this summer. Kenji Osaka is designing and testing it in Japan now. I put together my own Long Arm Conversion kit for the MSR X5T that uses all the stock buggy arms. You can read more about it on my website.
As for the Mugen shock & diff oils, you can get them from
Carolina's R/C as well as the ackerman. I run the KingHeadz ackerman. It is 5mm thick and has the 3mm in it for the reduced bump-steer. You should also buy a set of the new lower front arms and front uprights. They allow for 10% more turning. The kit comes with the gray springs. On rough tracks the light blue springs work great. I would also pick up a set of them to have as a tuning option. The rest of the car is SOLID!
Best of luck,