My bus has a 345, there should be a sticker like this under the hood, mine was behind the washer fluid bag.
Also in the glove box there should be a plate that gives this sort of information:
Cert. Net. H.P.: 182.3 @RPM:3800
Cert. Gr. H.P.: 196.7 @RPM:4000
Here is a site with a bunch of good info: