You'll definately want to do some porting on them if you do decide to get them. The intake side flows great, but the exhaust side needs a little work. You will be fine with a motorsport cam if you do some port work to even out the flow, but if not, then go after a split duration cam that favors the exhaust side.
$275 is way too much, when you can get them MUCH cheaper here
http://www.kellnet.com/chambers/
I bought a pair of bare P's + valves for $280 from them, not to shabby.
good luck,
-drew