We have a d318 power unit that I’m saving for a one off tractor project and it’s in restorable, but sad shape. We bought it from a friend along with a handful of tractors probably 15 years ago, and he had left the exhaust uncovered. Wt was a good runner, but due to the open exhaust, it was stuck. I have a parts book, but it says it’s for a different set of serial #s than what’s on the unit. Were there various runs of different 318s? Or would this parts manual work for this engine?         

That's a very late s/n D318. I can't quite read the s/n prefix but I suspect it is a 3Vxxxx series near the end of product of that run at s/n 3V16689.
I would get the correct parts manual as there are differences between tractor and Industrial engine, especially the lube system and pump and it appears to have the twin v-belt water pump and fan drive.

Thanks. Just scraped some more dirt off and found it’s a 5v. I found a manual on eBay for 20$ so I guess I’ll be buying some more literature!