So, I got my Accelero S3 in the mail today and after screwing around with it for a while I did manage to get it attached to my PNY GTX 970! I used the larger of the two sets of brackets and used the outer most screw holes on the brackets. These fit my 970 perfectly.
For those who may have to do this at some point, I have a couple tips:
First off, after removing the stock heatsink and shroud you'll want to be sure you secure the card's slot cover screw mounts to the PCB wherever the slot cover connected to the old shroud. You can either use a screw and a nut or in a pinch a screw and a matching motherboard stand-off work great.
Second, I have my doubts that this cooler would allow for passive cooling on a GTX 970, so plan on strapping a fan to it somehow.
Third, the placement of the various spacers included in this kit turned out to be VITAL. I had to use the 1mm white\transparent washers between the bracket and the screw nut. The 3mm spacers are too large and prevent the GPU from making contact with the heatsink. Without the 1mm washers though, the gap in the screw threads prevents them from being secure so you MUST use the 1mm washers here. I highly highly advise tightening the screw nuts to the bracket using a small set of pliers or wrench because it causes all kinds of problems if they unscrew while you're tightening the screw on the other end. I did put the super tiny 0.3mm black adhesive washers onto the card's PCB (heatsink side) around the outer set of screw holes to protect the PCB from the nut and to lessen chances of slippage.
On the back side of the card I opted not to use the back plate heatsink since it would have hit my CPU cooler. Much to my surprise, the screws stick out incredibly far from the back of the card... almost a full inch I'd guess. This causes two problems. The first being that the card just plain takes up more space. My sound card had been in the slot above my 970 but this would no longer work, so I had to move it to my bottom PCI-E slot (which isn't that far down since my old P67 still has 2 conventional PCI slots). Thankfully my only other PCI-E device is just a cable that connects to my USB 3.0 front panel, so that fit just fine above the 970 without the screws causing a problem. Still, it would have been nice if they'd included a shorter set of screws for those that weren't using the back plate because I wasn't really intending to move my sound card and now it is partially blocking the cooling fan for the GPU.
The second problem caused by the long screws on the back of the card (when not using the back plate heatsink) is that they actually stick out too far for the long thumb screws (manual refers to them as nuts) that you use to screw the whole thing together. Because of this I had to use both sets of spacers (3mm and 5.5mm) between the long thumb screws and the back side of the card. After figuring this out though, everything went together fairly easily. I could probably swap this off and back on in 5-10 minutes now.
Since I decided that I no longer care what my computer looks like inside as long as its quiet, cool, reliable and easy\cheap to maintain, I ghetto-rigged my 120mm Antec TrueQuiet UFO fan to the heatsink with carefully placed zip ties so that it'd be blowing partially over the VRM heatsink, I also used some more "creativity" and tethered the far end of the heatsink to a screw hole at the top of my tower with a super long twist tie. This wasn't necessary but I didn't like the added weight of the heatsink causing the card to hang down a bit. I don't want it to end up bent at some point. This worked very well. I just have to twist it to tighten it and now the card is level and doesn't budge at all.
After doing a couple other minor adjustments to make sure that my CPU and GPU fans weren't fighting each other, I did some testing. I didn't have a chance to do extensive "before" testing with the 80mm fan strapped to the stock heatsink but I know that it allowed my GPU to creep into the high 70s and low 80s in specific situations the other day. With the S3 and my Antec TrueQuiet set to high my system seemed to top out at around 67C in the same game, and its worth noting that the ambient temp in my office is much warmer today than it was when I tested with the stock heatsink. The sound is also much more pleasant than with the 80mm... though either is an astronomical improvement over the horrid noise the stock heatsink put out. My 970 is also idling at a chilly 30C right now as well, with a room temp around 22C.
For my needs, I think this cooler is fantastic. Hopefully I'll be able to keep this setup running quite a while longer. If I end up upgrading my motherboard+CPU eventually it should allow for a bit more room and I may end up using the S3's backplate for some extra cooling. I could probably do a bit of overclocking now too, should the need ever arise.
Fractal Design Define R6 - Ryzen 5 3600 - Gigabyte Aorus X570 Elite - 16GB DDR4-3000 - PNY GTX 970
IBM 5150 - Intel 8088 4.77Mhz + TinyTurbo 286 7.16Mhz - 256K onboard + AST SixPakPlus 384K - 20MB Miniscribe MFM - Everex EV-659 EGA + Parallel