Looks like you have been reading!!!
VERY GOOD INDEED!
When my motor is not in my trike its mounted on my mtb like this,
http://www.staton-inc.com/Details.asp?ProductID=3014
If you can find a rear mount / rack mount setup to buy you won't need the one for the in frame mount! (item #2 on your list).
We have one sponsor listed on the left side here that is in the final stages of testing a kit which is what you are leaning towards.
http://www.motoredbikes.com/showthread.php?t=8146
Keep in mind,,, this is the review of his proto type setup. Polishing and final adjustments are being made as we speak. Check with Him about availability.
I can only assume the reason that the other seller does not list the rear mount kit might be,
out of stock due to popularity, or inability to get the parts to make the kit, or it might be,, ???
The Staton kit is more money but I do highly recommend it to all who I talk to.
Read the details of what is included in your kit! The HD axle with the left hand freewheel is in my opinion the only way to go. and I believe that yes there is room on the right hand side for your freewheel. (NOT free hub)
Papa