best way...
The ideal set up is to have a gantry crane--looks like a kids swingset,only heavier duty--(and no swings!)..it has an I beam across the top,and two "A" shaped legs that are wide enough apart to drive under it..most use a chain falls to do the lifting,some have manual or power winches..
I have one made from 3" pipe that has proved indispenable for loading heavy stuff in my trucks bed..I use it a lot to put in and take out engines,and load things like my riding mower in the truck..It has an old hand crank winch off a junk boat trailer..(not the ideal kind,a worm gear winch is much safer,cant spin out of control when lowering a load--but I get by with it,being careful)..its nice to be able to load an ATV or mower by simply cranking it up,and backing under it with the truck..
You'll have to find the "balance point" as far as where to hook the straps to lift the body..I'd guess a K5 tub with doors weighs at least 1000 lbs,probably more!..I've scrapped many pickup cabs,they weigh about 400+ pounds,and an 8' bed weighs at least 300,so they aint lightweight!..
A blazer tub is pretty heavy,if it has seats and interior still in it..it COULD buckle the roof,but we lifted some off the frame at the boneyard with a forkloader carefully,and no damage occoured..we used 2 boards (2x12"s nailed together) as a "load spreader" ,and wrapped it with a heavy movers blanket to protect the doors --left the doors closed to help prevent flexing,and put the boards under the roof--they stuck out 8" from the doors,and we used some big 3/4"eye bolts on each side to hook the straps on..had to use another strap bolted to the rear quarters to keep it level as we lifted it,and to help carry the weight,so it wasn't all on the roof itself..as long as you dont "jerk" on the straps while picking it up,the roof should live..
We've done this in a shop by using a chain falls chained to one of the steel beams (rafters)..if you try it in your garage,I'd be sure it can handle the weight!..I've had to hastily nail 2x4's to my friends garage ceiling joists to the floor,to help hold them up while we pulled an engine once!--it was halfway out,and we started hearing creaky cracking noises!..
Another way is to use a couple of 4x6 "beams",wider than the tub by a foot or more on each side..after taking out the body mount bolts,bolt the beams to the body mounts just before the rear wheels,and the front ones under the floor,using long bolts, or threaded rods as studs,and wood blocks to make them lower than the sheet metal--some guys dont bother bolting them on,but I prefer too..
(You'll have to jack the body up some to do this of course--an engine hoist would be best,as it wont be in the way--using chain bolted to the rear body mounts will let you lift it without damage if your careful..a floor jack works,but is slower and clumsier)..if you only have a floor jack, just jack it up one side at a time,about 4" each,so it wont tip and slide off,and keep adding "cribbing" blocks or similar supports to hold the beams and the tub up..then you can roll the chassis out from under it..it'll take a better part of a day to do all of this,especially if your working alone (not a good idea,when doing this type of work!)..I've done it alone..hope I never have to again,alone or otherwise!..
