- as I am no suspension expert nor have used coil overs.
Looks as good as any but not inexpensive. You most likely want to use the front upper & lower tubular A-arms to go with the front coil overs as these have the added strength where the bottom of the coil over bolts up as opposed to your factory A-arms which are really not designed for any kind of load bearing pressure - even though you are still using a "coil" spring in conjunction with the coil over shock. I also believe the tubular A-arms are altered to provide better geometry for handling purposes.
Looks to be well engineered, but you will have to do some welding and the rear sway bar is mounted to the back and attaches to the rear frame which doesn't put your lower control arms in a bind (engineered my own version of this on my build because the Ford 9" did not allow for the use of the stock Pontiac rear sway bar).
There are other brands which use a tubular crossmember at the rear that has to be welded in so as to mount the connecting points for the rear coil overs. Global seems to have solved this in keeping the rear coil overs in where the stock spring goes along with additional bracing/supports to cover this.
You will most likely want to go with the adjustable/pivoting upper control arms. You want to "dial-in" the pinion angle and the factory non-adjustable upper control arms could pose a problem when going to the coil over system should it change any of the factory geometry at the axle.
has a much cheaper rear coil over version and is pretty straight forward in how it bolts up EXCEPT it bolts up at the top where your shocks normally would and this is too weak an area to use for this purpose - my opinion. Chevelle Rear Coil Over | A-Body Rear Coil Over | QA1 | 736-A-QSA
However, if you don't mind doing some bracing/welding to shore up this area, seeing you are doing frame off, it could be used. I braced up this area on my frame by fitting a few braces and welding it in. Not much holding that spring pocket to the main frame rail and seeing the rear shock is further back, I would be afraid of twisting/pulling out/fatigue cracking the metal.
Pictures show what I did to reinforce my shock mounts, but I think I would do a bit more if I were to use a coil over. You would still have to use a coil over set-up up front keeping in mind that the tubular set-up might be best as opposed to trying to beef up the lower control arm pockets -but it could be done if needed.
The advantage of the Spohn set-up would be that you could use stock boxed type lower control arms (or tubular if you so chose) fitted for the factory rear sway bar. Probably would not need the adjustable upper control arms as pinion angle geometry should not really change any - but it would still be a good option to consider.
Others may chime in with their opinion or experiences, but just do your research and even hunt around in some of the Chevelle A-body forums for ideas/opinions.