I have the Old Air system in my 54 truck and it works fine even in 100 degree temps. The reason I went with O/A was that the hose hookups are made on the engine compartment side of the firewall instead of under the dash. The plus side is that hanging the evaporator is a cinch but the hose fittings are obvious on the firewall.
Operationally, the O/A unit cools the cab quickly on a high fan setting and then you drop down to the lowest fan speed which is just above a whisper. I've used the other brands and it was difficult to carry on a conversation: not so with the O/A unit. In addition, the O/A kit includes the correct bracket to mount the compressor low with either the alternator or P/S pump above.
I elected to fabricate a pass side engine mount for the alternator and run the compressor and alternator off a dual groove pulley from Buffalo Enterprises. My unit is controlled with a manual cable which I consider to be the best setup. I have pictures of the install in my Webshots Chevy albums. Hope this helps.
Dave
