Yes, those exhaust bolts are probably the only thing wrong with the Gravely t-head design. The last Gravely I restored for a man had the port on the jug shredded. About $50 later I had a new exhaust machined.
Bob, I will warn you that is hard to date a Gravely except to within a generic period. For example, my L is approximately a 1955 just because of the oil system, but it also has a dipstick, oil bath air cleaner, slanted spark plug, a cast iron carburetor, and a white hood covering the gas tank. All of which are inconsistent with each other.
That doesn't mean, though, that any of these components aren't Gravely originals. Some tractors seem to be conglomerates of different eras, even documented since their purchase. Others are cobbled together by different owners replacing parts.
Knowing you have an L8 makes it easier to narrow down its age.
Ben W. in VA