The 2.3.20 link is :
TBH & MyDroidWorld Present: Droid 2 (2.3.20) Triple Threat
You also need RSD Lite. This will FLASH your Droid 2 to STOCK as it came from VZW.
I UNDERclock to save battery. The phone runs 2.0 Ghz but uses the same battery as the Droid 1 that ran 600 Mhz but I overclocked to 800 Mhz. It worked well. Since they BOTH use the same battery but the Droid 2 is faster it will use the battery faster. If I underclock to 800 Mhz it will last longer as I don't need the 2.0 Ghz speed 98% of the time. You can get SetCPU from the market. You cannot damage the phone by underclocking it. It will just slow the responce and speed.
As far as bootstrapping. It's a bit complex. But if you are a newbie. All you really need it for is backup and restore. If you make changes or switch Droid 2's you can install this app and it runs at boot up. Then you can backup or restore a previous backup. Once restored it's like it never happened. Look up Bootstrap for Droid 2 on the market.
Good luck man!