Emperor's Choice Games currently has free PDFs of a "subset" of Compleat Arduin; The Rules. I flipped through the original Arduin books in a game store back in the '70s, but was a little too wary and cash-poor (both continuing problems...) to actually buy them; my best friend in high school, who I gamed with, had previously played in an Arduin game, though, so I knew a little bit about it through him. This, of course, is not the original books, but a reworking of the rules into its own game system; I lack the experience to really tell you much about Compleat Arduin, but for those who want to sample at least some version of Arduin, I suppose this will do.
On a tangent from that, I'm aware that the original Arduin rules changed the way Fireball worked by dividing the damage rolled between all opponents in the target area. I'm wondering if something similar, but simpler, might be a good idea. Suppose that both Fireball and Lightning Bolt primarily target one individual, who takes full damage, and only occasionally damages other people?
For Fireball, those within 10 feet of the primary target take 3 dice of damage (the highest 3 dice of the damage already rolled,) minus one die of damage for every additional 10 feet of distance.
For Lightning Bolt, if the target dies or takes only half damage because of a save, the excess damage continues on in a straight line, possibly being reflected.