The QT diff protectors are friggin' awesome! I ordered them for a friend's D90 and they were installed by Dave's European here in Denver.
The rear is a direct bolt on, but the front requires some mounting tabs to be welded on, then it's bolt on
I know you said you didn't want a weld on, but even if you go with another manufacturer that bolts on, you should still at least have it tacked on, otherwise you will knock if off the first time you hit it (the front that is).
I ordered from here:Discount British Parts.com
click on "specials"
Here's an excellent install writeup from the OKRovers website:QTServices Diff guard install
I just noticed while typing this reply that the install on the OKRovers website is for a Disco II. The front diff guard I received came with tabs that were welded on (to a D90 front diff), just like the ones shown in the photos. It is possible that I received the DII diff guard instead of the one made for the the D90 which (according to QT's website) just bolts on without welding the tabs on. Either way, this is the best front guard I've seen to date and it was tested a few weeks after install and did exacty what it was supposed to do.
I'd advise calling Discount British and asking if welding is required.
Best of luck,