theres a guy on club4ag that sells the bellhousing - his name is toycoolrolla I think, infact I think the guy sells a complete kit. I bought a 4ag to w58 bellhousing from him a while back. Theres also toysport like bill said above. I also have that friend up in georgia that was doing this swap, I could check up on his progress for you.
totally custom motor mounts... unless you buy a kit I guess, Yeah the suspention will hold it fine, the 3s isn't really that heavy of a motor, but of course the chassis is designed for 100hp and some reinforcement will be inorder.
A while back I saw a complete altezza clip on ebay for like 3500, I think they are in fairly low demand, so one may be bought cheaply, if one of those can be found it would be ideal (not the same motor as our is300 - think s2000 motor).
I'm doing some crazy custom stuff to my hachi (lets just say it involves various supra parts and a lysholm...) my aim is toyotageoffrie if you want to talk about it.
-Jeff