I found a Truck to look at

[D.PASSMORE]

Overall, looks OE in their, no heat stove from the drivers side manifold to bottom of air cleaner. On the A/C vacuum ball - their should be a bracket holding it out not bolted directly to box. There is a two A/C brackets missing - one on the rear of the A/C compressor and the other bolts to the Intake manifold - they connect to stabilize the Compressor on the back side. A lot of wires hanging out too. But it appears to be the correct system for that Blazer. The last issue would be if it was non-A/C vehicle and some one put a OE '72 system on the truck, then there would have to be a lot of modifications to the firewall and dash areas. So, the question would be - quality of work. Last ensure that the title, VIN plate, frame and SPID are match numbers.