go for it ken,*you'll never regret it.
based on my experience, if you are working *evenings and weekends, then using the prefab will save at least*6 to 8*weeks off of the construction process. also, with the pompeii, it is difficult to exactly end up with the desired height of the dome (my oven probably ended up more as a Tuscan than a Neopolitan because i overshot the height). that obviously isn't a problem with the pre-fab. given, the difference in cost between the firebrick and the pre-fab, i'm sure i was building my oven for about minimum wage. (ahhh, but the pleasure of breathing brick dust).
that said, you are about a 90 minute drive from my pompeii and you are welcome to**"come on down" and take a look at my base, landing*and dome treatment.*
my oven pictures are at <http://www.cpsusa.com/ebay/pompeiioven.htm>
www.cpsusa.com/ebay/pompeiioven.htm