I have had several vehicles with A6 compressors and they put out a massive amount of cold air - when they were working properly. The problem with them is that they shoot out copious amounts of oil. Alma Products claims to have fixed that problem. Of course, they do suck some horsepower and penalize mpg, but if you own a 454 you have already given up on fuel economy.
A6 compressors are still used in new heavy equipment (dozers, excavators, etc.) so somebody still thinks they have a purpose.
There are several places to get Sanden adapters for 454s, but I have had trouble keeping the belt quiet with my heavy one piece steel factory bracket, so I don't think the two piece sheet metal adapters would be very steady. They look like something I would make with tin snips and a jig saw in my backyard. This is what they look like.
https://www.speedwaymotors.com/Vinta...vy,256916.html
https://www.summitracing.com/parts/b...make/chevrolet
https://www.speedwaymotors.com/shop/...10-4-461-14796
There is another option - the lightweight S6 compressor, which the local A/C shops around here will not install because of no history with this compressor. I have read some bad reviews on it. It appears to be just an A6 in a lightweight housing, and they are not cheap, so I think I would prefer a new Alma A6.
BTW, my local A/C shop told me my DIY Geo Metro pusher fan which works when the compressor turns on does nothing to help the A/C perform better. He said it did no harm but did no good either. I guess his idea is that it is not necessary with a properly performing system, and I would agree, since I have had several A6 systems which did not need any supplemental help.