You can fit the lipos to most car, even the square ones... damn, you can even fit it to some saddle pack cars if you're creative since there's one in an XRay on my review of the trakpower 4900mah pack.
http://www.oople.com/rc/photos/reviewtrakpowerlipo/
I think orion do a pack which will sit into the slots, but I don't think its generally a problem as long as there's clearance for the square shape of the pack it should be cool.. It's not as heavy as a nimh pack so even if you're taping it in and it 'looks' less secure, the fact it's lighter means it's less likely to get thrown out - if you get my drift.
I found racing touring with a lipo quite enjoyable - the car was ultra competitive and easy to work on (just left the pack in and kept recharging it between rounds)