Yesterday I picked up a GMC 270 inline 6. It's complete but internal condition is unknown ... haven't got to fiddle with it yet. A HAMB search brought up some good info on older threads. I now know how to date the engine and where the casting numbers are when I manage to scrape down to them! It is a military engine, and has a rebuild tag from the Red River Arsenal dated 1951. (see pics). The head casting number, 6107412, puts it in the 1939 - 52 category, so I guess it's safe to assume a late '40s production date. A web search took me to several WWII military vehicle sites, primarily dealing with CCKW variants, (the venerable "deuce and a half"), and also the DUKW amphibious vehicles. On more than one of these sites, owners are strongly cautioned not to exceed maximum rpms for any length of time, promising dire consequences. Max rpms in this case being about 2750 for earlier engines, and a little over 3000 on later ones. So my question is ... is there something inherently weak about the military engines as opposed to the civilian versions, and if so, what? I would assume (ha ... there's that word!), that the rotating assembly and rods would be pretty sturdy, and that any possible weak points would involve the pistons, or possibly the valve train. Any input would be appreciated .... thanks!