Well, I finally took the plunge and did the mod on my 7970. I used h100i and Dwood's bracket. So here's a small report in 5 parts.
Part 1: A tale of three CLCs
I ordered and received the Dwood bracket late last year, and it took me this long before I finally had the opportunity to build a new rig based on 3570k in P280. I actually ordered 3 different water coolers, H100i, antec 620, and thermaltake water 2.0 pumps. My intention was to find CLC with the quietest pump, and that turned out to be H100i. The Antec 620 and Thermaltake 2.0 both use round asetek pump and both have "horrendously" loud tick when they're turned upside down just like they would when mounted on a videocard in a traditional case. Now, "horrendously" may be a slight exaggeration, but noise is subjective, and to me the ticking noise was clearly noticeable over my ambient noise level. I tried everything to get rid of the ticking noise, I tried slight pump downvolting, I tried shaking them, tapping them, magnet tricks, I left them running for couple of hours hoping for noise to go away, and at all times I always positioned the pump and radiator in such a way that no bubbles would be going through the loop, nothing helped. So personally, I drew a conclusions that asetek pumps are no good. Luckily, H100i turned out to be very quiet in open air, and nearly silent inside the case.
Part 2: The installation ordeal
To be honest, installation was a major pain. It took me better part of the day to get everything working. The fact that I had to spend probably about an hour on the bracket itself to make it fit didn't help. First I dremeled out Dwood's logo from the fan portion of the bracket because I didn't want anything impeding the airflow making it noisier than it should. Then I had to file down machining marks around the GPU portion because otherwise the bracket would not fit over the 7970 GPU protective shim. Even after doing all that, the bracket still wouldn't fit the card. The problem was that when the bracket was mounted on the H100i water block, the bolts that are supposed to attach the water block to the videocard were not completely "sunk" in the bracket and H100i block pushed them into a converging pattern, basically, the bolts would not alight with the GPU mounting holed on the 7970 PCB. Had to fix that too. In the end I made it fit, but it took me a lot of time. I literally spent 6+ hours trying to make everything work.
Part 3: Where we learn that the prettiest shim is not always the best
The 7970 with their recessed GPU cores need a shim to properly transmit heat from the core to the waterblock. I tried two shims for the GPU - one from EK-VGA and one from Dwood. I tried EK-VGA shim first, but computer wouldn't even boot with videocard plugged in. The fans would spin for split second and then everything would shut down again. I took a closer look, and it appears the EK-VGA shim is so thin that it does not leave any space between Dwood bracket and PCB. With EK-VGA shim in place the bracket actually touches the PCB. I suspect the bracket was shorting some of the contacts on the PCB and the video card was shutting the whole thing down to protect itself. So I had to take everything apart yet again and install Dwood shim. Dwood shim did not look nearly as nice as EK-VGA as it is significantly thicker, but it did the trick. With Dwood shim in place the bracket was not touching PCB and everything worked without any fuss.
Part 4: The Triumph... sort of...
When all said and done, I have mixed feelings about the project. Before I mounted H100i on my 7970, I was actually running it with custom modified Accelero S1. The H100i definitely runs better, but not THAT much better. In both cases I ran two 120mm 800RPM Scythe S-FLEX SFF21D fans. I'm not that much into overclocking, so I run my 7970 at 950Mhz. My card also has stupid high default voltage of 1.174V on the core. When downvolted to 1V at 950MHz and with two 800rpm Scythes on Accelero S1 my card hit around 78-80 degrees full load. With h100i, the same 950Mhz, the same 800RPM Scythes in pull configuration, and 1.038 core (slight bump) it hits 72-78 at full load depending on ambient temperature. So h100i solution is better since I have lower temps and slightly higher vcore, however I kind of anticipated better results.
Part 4: Epilogue
There are a couple of lessons to be had from my experience. First, I wouldn't trust any asetek based CLCs. Corsair pumps are quieter, at least in my experience. Second, when installing the mod, make sure the bracket does not touch the PCB. Third, and last, don't expect any miracles, yes, The Mod is much better than stock solution, but it's not that much better than other aftermarket stuff, plan your expectations accordingly.