It is a gas burner. It has spark plugs and a carburetor. I think it is probably a 1950 model. I think 51 or 52 was the last year the the 520 was produced. The book calls for a 318 cu in engine. 3 7/8" bore by 4 1/2" stroke. The truck is still on the trailer and it is a misty rain today so I'm not climbing around on it today. I fell off of trucks with butterfly hoods when I was in my 20's. I certainly don't need to climb around on one thats wet and on an trailer now that I am in my 70's.
If I remember correctly, the big bore family from the 318 up to the 503 are all bolt ins like the 228 to 302 on the small block engines.
That model always fascinated me the way GMC took a pickup cab and made a truck out of it. I think it was only the 520 and 630 series that were done like this. The 700 series and larger is what we called the fat cab and they never really excited me.
