You can get A/C on a 67-72 so no need to go long pump for that. I would not use an A6 compressor, but there are kits to put a Sanden on which will have the brackets you need anyway. And if you do go serpentine, get one without an R4 compressor like a Corvette with Nippendenso or the later 4.3 or 5.7 with the silver compressor and then get a Nippendenso to replace it (not an offshore). With any of these you will need a different alternator and I would want a CS144 not a CS130.
https://www.classicindustries.com/pr...Gmph3crLtlBrGx[/QUOTE]
This is the set up I found yesterday that I was thinking about going to/using.[/QUOTE]
That is an R4 compressor. In my experience they do not like to sit. If you use it very regularly and defrost in winter it will be OK. If you park it in Winter and never use defrost and it sits for months, you may have seal issues.
Early C4 Corvettes use a similar setup with R4. Later C4 (Tuned Port, not LT1) use a Nippendenso compressor.
If you must have serpentine, I would look on late 4.3 S10 Blazers. They have the silver compressor. The offshore new ones are junk but the real Nippendenso ones hold up pretty well. Whatever you do you will need new hoses. I put a Corvette R4 setup on a '72 for a guy once and made the factory hose work but it was really too tight since the R4 is shorter than an A6.
Also, lots of late blocks have roller cam provisions. Yours has provisions but has a flat tappet camshaft. I would not tear down a new crate to change the cam but that's me. The flat cam will be fine if broken in right IMHO.