On the bi-level SIR system, is the front section the same height as the flat-top like on the KAC RAS?  I know the reciever section has a riser like the #45, but I don't know about the bi-level (the number of which escapes me right now.)

you are right I do believe.  The bi-level is the same height as the flattop.

     Max

Here's the mid-length #58:

[img]http://photos.ar15.com/ImageGallery/IG_LoadImage.asp?iImageUnq=11903[/img]
Photo courtesy of MSTN, on the EE

and the thread that goes w/ it, BTW MSTN sells the #50 too, which, IIRC is the carbine length, check w/ him he'll fix ya up.

[url]http://www.ar15.com/forums/topic.html?b=7&f=22&t=165621&w=searchPop[/url]

Front section IS, just as you described (level w/ the flat-top) and designed for having the EOTech sight positioned out over the handguard at co-witness height.

Mike