well if tinkering is what you want to do, the 6.2 or 6.5 is a great choice. they are cheap and very simple to work on. early 6.2 engines [82'/83'] had some head gasket issues. get the uprgade headbolt, problem solved. harmonic balancers with lot of age or miles can as mentioned lead to stress cracks, or more likely a broke crank shaft. this applies to both the 6.2 and 6.5 engines. 6.2 engines will pull any load a 350 will pull, add a turbo and it will run with a stock 454, [pre vortec]. i have/had both, as well as hauled alongside others. the 6.5 is a decent puller also, stick with the mechanical engines for reliability, computerized one's had some issues. wether 6.2 or 6.5, something to keep in mind, if it has a turbo, keep a close eye on egt's. 6.5 engines have a lillte think crowned piston, but both are subject to cracking from excess egt's, too often. rings get brittle also. as for maintnance, both will hold up better then any powerstroke when it comes to poor maintance. my oldest 6.2 had nearly 400k on it before breaking a crank [ see balancer advise] , and it had seen several 12/15k mile oil changes. after nearly a million miles of seat time behind trucks powered with these engines, not a single one left me stranded. i have used them exclusively in my farming and construction buisness, hauling anything from 1500lb hayrakes to 15000lb backhoes , frequently. while i would rather use one of my fords or dodges to do the serious towing these days, i still remember the time when a turboed 6.2 had to do all the pulling, and i still use it on ocassion.