More pictures here & info:
http://www.rc-monster.com/forum/showthread.php?t=15176
and another, bit more info I think:
http://www.rc-monster.com/forum/showthread.php?t=14247
It is a fairly simple conversion I believe, but you will have to use the assembly manual posted here on RCM (somewhere, maybe...) as FLM dont provide one usually.
I think everything you need is included, just a case of asembling it & mounting all the flux parts. You wont have/need the brake parts & servo, or the reverse mechanism & servo etc.
Check Joram's thread (2nd one) for lipo dimensions, but it seems you can adjust the motor mount position a bit to accomodate pretty much anything- 5s 4000mah should fit fine- you can even widen the chassis a little with some shims to fit fatter packs.
Flux motor will fit fine, even with those fairly long fins.
Having the tranny up front shifts some weight up front, and having the motor in the middle & the lipos in the rear makes the truck pretty well balanced front/rear I believe. Since its a bashing truck really having perfect handling isnt 100% vital, but I dont think you will have any issues with the truck being hard to steer, just give it a good strong servo