I'll see if I can dig up the old files and figure out what all I changed for the SM Bikes pack. I've had a few requests to update it and I think it's just time to do so. The two stroke SM's were a ton of fun on kart tracks, the engine character of the 250X made rolling it on at apex build into the power band by corner exit, and clicking up the gearbox as you run into the strait sections, was super rewarding.
The 650 was based on my friends XR650L (not your grandpa's 650L!) that has a Wossner piston (683cc), Hot Cams Stage 1 cam, extensive port work to match the oversize valves (can't remember how much bigger they were, but they took up alot of real estate in that head!) and a flat slide carb on an opened up airbox with an intake boot that fitted the flat slide to the airbox proper. IIRC the gearing is +1 front and -3 rear (custom rear sprocket) and it still wants to float the front tire in 3rd gear. Honestly it's as close to a XR650R as you will ever get with the L model. Seeing it represented in game, and able to pick up the wheelies at the same speeds that my friends bike does, was pretty incredible. I've been bugging him to put supermoto hoops on it for years.

I'll try to find some time to update the pack and get online. The latest MXB beta is fantastic at low speeds on kart courses, and some of the RX tracks that have been released are really good with the dirt physics and air control that has been straitened out.
Did a loooooong wheelie on the last beta with the standard 450SM.
https://www.youtube.com/v/vJTiUUQ6B_c