I had a 71 and I'm pretty sure you could sleep in it if you took the back seat out. Unlike newer vehicles that have a passenger footwell and a folding or tumbling seat, the Blazer back seat is a single unit bolted to the floor. Unbolt it and you have a completely flat load deck from the back of the front seats to the tailgate. The 67-71 also have the IMO superior lift/drop gate (i.e. two piece gate where the top lifts up and the gate drops.) By contrast the 73-89?90? Blazer has the roll-down window, which is OK unless the regulator breaks because then you cannot open the tailgate at all. Our Army CUCV M-1009's were diesel Blazers of this vintage and the broken regulator was a common problem (mainly due to misuse/abuse.)
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To answer your other question, no they never made the Blazer in multiple lengths but the Suburban is basically a longer version of the same thing. There are a few other differences, the biggest one being that the Blazer had a removable fiberglass top while the Suburban did not. The Suburban's of that vintage had a very unusual "3 door" configuration where they had only a single door on the driver's side but had two doors on the passenger side. These are typically referred to as "3 door suburbans." The only other vehicle I'm aware of that had a door configuration like that was the 1957 - 59 International Travelall (My very first vehicle was a 1957 3 door 4x4 Travelall.)
