Is there a ServUO for supporting Ultima Online ™ - Lord Blackthorn's Revenge [3.0.6J] ?

You can switch the Expansion in ServUO P57 and earlier versions; you can go back in time via the github repository to grab the entire project in any state for that time period - maybe P55 would be best suited to your needs.

You could also grab the last release of the original RunUO 2.7 which would is around the same in terms of codebase, as ServUO 55 was.

The actual formulas and mechanics of pre-AOS eras are subject to debate on accuracy no matter which project you use.