[wkrtsm]

You'll need to reinforce the shock towers on the crossmember if you use coilovers in the rear, since there's a history of cracks/tears in the metal on the tower itself and where the crossmember joins the chassis main in the rear engine bay. Going to coilovers involves a torsion bar delete, and the shock towers were not designed to carry the full rear weight of the chassis+engine+transaxle (like the torsion bars were via the spring plates).

Rear coilover choice is a personal preference based on your own due-diligence (research, purchase choice). You have a long wheelbase (LWB) car, and I believe as long as you order coilovers for an early LWB car, you should be good to go. I don't think aluminum vs steel ('69-71) LWB trailing arms matter, since the angle of the shock tower was likely not changed when going from steel LWB arms to aluminum.