Just got done doing the valves on my beater '83 SD, and cannot believe the difference! It's been on my get-to list for awhile, but got caught up in other stuff, and have been driving my nice SD since getting it back from the ex. They were all extremely tight, and it has made an instant change it the way it starts and runs. Before it would always start on the first crank, but if you didn't keep it floored it would stall out and die and need to be restarted, and blow white, fuel smelling smoke, refuse to rev above 800-900 rpm, then after 15 seconds or so fully rev, but would still mildly blow smoke until fully heated up.
Now it starts, idles smoothly, no smoke, revs fully, and generally runs great, with better power on the low end. I think they were so tight that one or two of the cylinders weren't even firing until it heating up after running for a minute or two. So, to anybody stalling on getting around to the valves, GET ON IT! You'll be glad you did if it's anything like mine....checked the chain stretch while I was in there by the admittedly crude method of lining up the assembly marks, looked to be under 3 degrees, and the guides looked good.

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater