I had a quick look around for barrels but the only ones I found needed replating anyway or were new and cost ~$1,000 each. At that price you're better replating or going with the 300 kit. Hopefully others will come up with some idea.

Matt may machine them for you - you'd have to ask. Best to let him do the work as he's done enough of these to know what he's doing. The porting is changed too, so if you just whack on a 150 barrel don't expect it to go very well, supposedly the first of the 300's was slower than a 250.

Anyway, if you aren't planning on keeping it stock, I'd say go with the 300 kit, it's very nice and despite what people say, it revs out to 13k even with the ART pistons.