The originals had E-185's, most upgraded to 205 HP. A few came with 225's but many were upgraded (it didn't require any modifications to do so). Then as Bonanzas got bigger engines, so did the Navions. Ryan beefed up the fuelage a bit allowing 260HP GO-435 or IO-470's. The last of the Canopy models was approved for IO-520s. The Rangemasters came with IO-470,520, and 550 options.
Starting the engine is one thing, flying it is quite another. I can almost guarantee the prop on it is subject to some onerous ADs. If it's the Hartzell (most likely), if it is the double shoulder X or V hub, it needs an inspection, but in all liklihood it's unairworthy. The Macaulay prop is probably officially end-of-lifed.
E-225 parts are getting pretty darned scarce. Most have bit the bullet and put one of the injected Conts. in.
In addition to the problems with the engine, I can bet that the thing has a pS-5c presure carb and all the rubber in that is shot.
I can also bet that the fuel hoses probably are about as brittle as all gitout. I found one on my plane dated 1948 (amusing since mine is a 1950 model).
Yep, the prop diaphram probably needs to be replaced. You can start it, but I wouldn't plan on running the engine too long. I was getting good at changing prop diaphrams until I got rid of the gopher engine in mine.
If it's been parked for five years, it almost certainly is subject to the Navion moronic fuel valve AD. The good news is that other than the prop and the fuel valve, Navions haven't had ADs on them since the 60's I think and none of those were real onerous anyhow.