Ah, I just downloaded the file I'd linked from shipped-ROMs to check what was in there. The RUU.exe is in it, it's just inside a zip inside the zip.
So the development thread for beanstalk is
here. Ignore the image of the Nexus One, this is for the Desire. The two will be quite different, as you can probably tell from the screenshots on that page, since Beanstalk is not based on HTC software so won't have the HTC user interface or apps. If you want to use the Play Store Beanstalk might be better, since I can't remember whether Gingerbread is supported any more (might be, but it's very old), and there may be more apps that are compatible with it - though there will be many apps which don't work with either. I've never used this ROM so can't say how well it works.
The key thing is to look at the "instructions" in the first post of that thread. If you never did any hboot flashing (which is how you change storage partitions) then you should be able to use either ROM, since this Beanstalk needs a stock or near stock partition table. You will need a custom recovery in order to install it, but fortunately the thread has links to those and although I've not downloaded the files it looks like they are hosted by XDA and so are probably still live. I used to use 4Ext recovery with my Desire, which is also capable of partitioning an SD card (so if you don't want to set up the GNU Partition Editor, GParted, that might be the way to go if you choose Beanstalk). The reason it says you must partition the SD card is that it will use the second partition as expansion of the phone's storage (some ROMs use it to fit part of the ROM, but I don't
think this is one of those). That will give you more space for apps, but there is some fiddling required to set it up. And with the exception of 4Ext recovery itself, which they've packaged as a PB99IMG, all of the other stuff is installed (flashed) using the custom recovery, including the ROM.
My advice: if you want to try that back up anything important on your SD card (as that will be wiped by partitioning), read the instructions carefully and don't start until you are sure you understand every step and have made sure you can download all of the necessary files (i.e. that they do all still exist).
One thing to consider is that there's no guarantee that flashing the Beanstalk ROM will solve your problem. It really depends on what is causing the bootloop. That is also true of the RUU, except that if the RUU doesn't fix it then nothing else you do will. It might be worth installing the recovery and doing a factory reset (or even trying to do it using the HTC recovery), just to see if that fixes it, then consider what you want to do next. If you want to try Beanstalk I think I'd try that first: you can certainly run the RUU afterwards if it doesn't work, but I'm not 100% certain that you'll be able to install Beanstalk after the RUU. The reason I say that is that while I cannot remember how Revolutionary (the tool you used to get S-Off) worked, the fact that your hboot screen says "Revolutionary" at the top suggests that it replaced the hboot. And if that replacement is important it's possible that the RUU will break it, since the RUU will replace everything, including the hboot. And the Revolutionary tool no longer works, so it won't be possible to run that again even if you have a copy of the tool (unless you also saved the "key" that it requires, since you can no longer get one of those). Hence there's a risk that the Gingerbread RUU will be an irreversible step (may not be: on later HTCs S-Off status was not affected by running an RUU, but the way this stuff was done for the Desire was a bit more "hacky" so that possibility remains).
There is one other RUU that might work, which is the one you get if you go to HTCDev.com and follow the
unlock bootloader links. For the Desire that gives you a special RUU (based on Android 2.2) whose bootloader can be officially unlocked, allowing you to use fastboot to install a custom recovery. This does not grant S-Off, and prevented you from ever gaining it, so we didn't use to recommend this, but if you were to lose S-Off status you could consider this one to see whether it at least gives you the option of flashing a ROM. I don't remember whether it works if you've already flashed the 2.3 RUU, or conversely whether the 2.3 RUU works if you've flashed this one, or even whether flashing either precludes the other, so I'm just putting this out there for completeness. As I said earlier, if you are interested in a custom ROM I'd try that first before trying an RUU, but it may be that you need an RUU to get the phone working (or indeed that the problem is a hardware failure, in which case not even an RUU will help).