Well, I've experienced two of the three options myself (no shackle flip experience). Originally had blocks under the Blazer I just sold, and also had blocks under all four of my other K5's, and then put 4" lift springs under the Blazer a year and a half ago. My issue is I want the Burb to ride as well as it does today, which is truly excellent, and have the same towing capacity as it does today. Lift springs do not ride as well as stockers, from my K5 experience. It didn't ride bad (and they were Tuff Country 4" rear springs, with all poly bushings, etc) but it was not as good as stock with blocks. Axle wrap was gone after the spring lift and I would consider that the best thing about the all spring lift. /forums/images/graemlins/tongue.gif That, and knowing that you no longer have (in my 79 K5's case) 22 year old springs/bolts/bushings, etc. Nice to have that 'all new from the frame down' peace of mind.
Think I'll start off with blocks in the rear, can get a set for free and only be out the U-bolts............then if I don't like the axle wrap (if I get any) I can always put lift springs in. /forums/images/graemlins/laugh.gif