I just finished the accessory drive on my 68 vette.
Simple, only needed a AC and alternator drive. I added the 2 idler pulleys at the last minute to be sure I got enough belt wrap around the balancer. The belt is tensioned by the alternator swinging up and away from the engine.

 

What idler pullies did you use? I only see two connection points on the alternator. What is stopping the alternator from pivoting and falling down? Is the bottom bolt a thru bolt?

 

I used 2 standard idlers (70mm F body ribbed, and Gates #38018 70mm smooth). They're mounted to the water pump tensioner bolt holes.
The alternator pivots on a spacer block through a head bolt hole. The spacer is monted on the 2 outside head bolt holes. There's an adjustable upper arm link that swings the alternator up and out to be used as a tensioner. It also had some flex in the alternator, so I added another link to the front bolt hole of the alternator to stabilize it.
The alternator works like the SBC setup.
I've got about $100 in it, but $70 of that is in the 2 adjustable rod ends. I tried using the SBC stuff, but there was too much flex.

 

the ac plate is out of aluminum i would assume? why plate that insead of adjustable arms? so you'd have mounting points for the idlers?

 

Aluminum plates costs me $0, and the plates are very solid. You could probably lift the motor by one of those plates. The added idlers were just in case of slippage without enough crank ballancer wrap.
I used adjusters on the alternator simply so I could have adjustment without a spring tensioner.

 

Looks good...I love innovation.

 

cool

 

cant see pics

 

do you have a pic from the top?

 

I'll shoot a few tomorrow. It was set up to use the truck accessories and mechanical fan, so I fitted an air tube to use a cowl intake.
Pics to come.

 

Great job!

How thick does an aluminum plate need to be for this type of application?

 

I used 1/4" plate for both the front and reat Vintage Air AC compressor plate. I had to add a 1mm spacer plate to get the compressor to align with the crank pulley grooves.
The difficult part with old vettes is keeping the accessories under the hood, but not having belt interference problems with the vetttes A arms.

 

I take it you are running a manual steering box?

very cool

 

Yep, manual steering. I do about 90% hiway, so power steering was not worth the cost or effort.

 

Top images.
Alternator mount:

Vintage Air compressor:

The whole thing with fan:

 

Just curious, it looks like you are running and F body water pump with a truck style pulley. Are you going to run the mechanical fan or electric? What is your plan for running the upper radiator hose without interfering with the mechanical fan?

 

Yep, I swapped the pulleys on the water pump. I'm running a mechanical fan with an electric one too that's actuated by engine temp or the AC compressor. I cut off the top outlet so I can run the hose inside and around the fan.

 

looks good

 

Is that all that holds it up, the 2 adjustable rods? Or is there a third mount in the rear?

 

Looks to me like the lower adjustable rod has a bolt that goes through it, the alternator and then into the head.