you could basically use any engine in your truck up to now really. the old school blocks up to the 90's bolt up, stock and then the ls1 type engines and such have adapter plates. SO if that's what you wonder basically anything, but to give you a guestimate, up to 98 chevy or gmc 2wd or 4x4. 86 and up use a 1 piece rear main seal, so make sure to use a flywheel/flexplate that goes with the motor, or buy one that fits it.
You could go way back as well, almost to the start pretty much of chevy v8 like around the 50's 60's or something. As mentioned the oil dipstick switches sides but there's no worries there, they'll physically bolt up, the newer block though some cannot use the block mounted fuel pump. You can make it work though, with electric pumps or something, so basically you are limited only by your skills and what you want or are willing to change. As for an almost direct bolt in drop in deal, I'd say 73-87 or even older, like maybe to 67 or so.
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