If it's not too late to weigh in... Me being a former Master Detroit Diesel Guild member of 20+ years, may I ask does this truck have an Inline 6-71 or an 8V-71? Reason I'm asking is when doing an in-frame overhaul if you're truly considering a turbo install you need to be aware that most inside parts that will be changed will need to be changed to accept a turbo. The camshafts are different, the gear train timing may need to be changed (Which means the flywheel housing needs to come off to reposition gears to proper timing marks.) the piston crowns are different compression (If they are not changed to the lower compression the fire rings will fail very quickly from to much heat.) and lastly, some of the GMC Brigadiers had body changes to allow the turbo and exhaust pipes to fit. The cylinder heads should be ok as far as valve material unless this engine has the original head. They changed the valve material in the late 1980's to make them all turbo safe but prior to that the naturally aspirated engine valves were a softer material and would fail prematurely with the higher heat of a turbo.
I'm not saying don't do the job, just make sure you build it right or you will hate life in the long run on the Detroit Diesels.
Good Luck and please don't be afraid to ask questions.
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