When I first started at KDOT (Kansas) we were still doing this same procedure. Both mixing on the road and laying already made material. We had a little more traffic control, but there was a little more traffic than these guys have. I think the traffic was a lot nicer then too!!
You had to be an operator then not just a driver. 
 

Hi, Neil.
Cat went to diesel engines in their graders very early on. I think that the first unit shown is a single drive Cat #11 and may have had a gas engine but I would suspect it had a diesel even back when it was built. There is also a tandem drive Cat #11 which again likely had a diesel engine. The rest of the cat graders appear to be #12s which would also most likely have had diesel engines. There was one model of the #12 built with a gas engine, I think, series 6M, but that didn't last long

Among the 'oddballs', I did see a Galion which appears to have an International engine, likely a gas-start diesel, and an Allis Chalmers grader, model and motor unknown.

The Galion was hydraulic controlled . they built their first hydraulic controlled grader in 1925 - while the rest were gear controlled.

Just my 0.02.

AC used Detroit Diesel as their diesel engine in big equipment until 1956 or 7 when they switched to Buda which they bought several years latter. One of AC's early self propelled graders had the gas engine they used in a model M tractor.

Hi, Ray54.
I shoulda remembered about A-C using 'drip-troits' that late. Thanks for the heads-up. The only A-C grader that I ever operated was a 45 and I think It had a Buda diesel. I don't know the build date of that unit as I was only on it for about 6 hours trimming a sandy building site in about 1967.

Just my 0.02