Mongoose's website did give me the seatpost diameter, 31.6 mm. And I have my buddy at the LBS helping me out, getting a good price on a salsa seatpost and stem. Getting a used Easton riser bar for ultra cheap. Mongoose customer service is fairly useless, they aparently don't have specific owners manuals with specific Info to each model, just one generic overview that is supposed to cover the high end stuff as well as the low end stuff. While the frame itself looks excellent, and I am confident in the build quality and design, the people at mongoose don't know much of anything about their bikes.
The frame came to me with a headset, and rear shock... That is all, I know it come with an external BB, so what I am trying to determine is the proper spindle length required to keep the cranks at the proper space off the frame for the chainline, and front deraileur function (no rub and accurate shifting) i have no idea what it should be, and mongoose doesn't tell me anything useful! Ugh! Oh well... I am going to mount up a rear wheel, and pull a stringline off the middle cog, and do my best to determine a good spindle length for my bottom bracket... I will keep you updated.