You know, until reading this it never once occurred to me how treasure division could mess up xp awarding, as despite gobs of 1e or 1e-based experience I've never in my life used (or played in a game that used) xp-for-gp.
How do I give out xp?
Combat or significant encounters: tracked individually, thus if characters A, B and E are the only ones involved in a particular encounter, characters C and D don't get any xp for it. After each encounter I just put a tick next to the name of each character who was involved, and a note as to what the encounter was; sometimes I'll note "half" if someone's involvement was only peripheral or if the character died during that encounter.
Every now and then I go through, do all the calculations, and hand out xp; if nobody's close to bumping it can be a fair number of sessions between xp batches. PCs can only gain xp after a night's rest. If I know someone's close I'll give 'em out each in-game morning, which can sometimes mean more than once in a session.
Dungeon or adventure bonus: after the end of each mission or dungeon or adventure I give out a bonus. In a small way this kind of makes up for not getting xp for treasure, and its intent is to reflect the xp earned for all the little mundane-ish things e.g. finding water, making camp, mapping, etc. that would be just too tedious to track all the time. The amount each character gets is usually about in proportion to how much of the adventure that character was around for, thus a character that came into an adventure halfway through would only get half bonus.
Bonus is only given out after the adventure is finished; and characters who died partway through still get their bonus share, which leads to the odd situation of characters occasionally bumping while they are dead!
There's no real hard-and-fast formula for calculating the actual bonus amount; usually I'll start with about 1000 x [the party's average level] and adjust up or down from there based on adventure size/length/importance, how xp-rich or not the adventure has already been, how successful the mission was (for a mission-based adventure), etc., etc. - i.e. there's a lot of 'eyeball' involved.
Situational: this is a catch-all for other things. Thieves get xp for what they steal (sometimes including from the party but only if they don't get caught; and this does not include skimming off of found treasure). Goodly types get xp for doing goodly deeds outside of adventuring. Sometimes casters get xp the first time they cast a significant spell e.g.
Raise Dead or
Commune. Just about anyone gets xp if they happen to meet a deity or other uber-important being and survive the experience. Etc.
After you bump: characters get partial benefits right away when they bump, most notably they roll their new level's hit points on the spot and get access to half right then; with the other half (and most other level-up benefits) coming only on completion of training. Unlike RAW 1e where advancement stops dead on bumping, here it can continue as normal for a while; but if you get 1/3 of the way through your new level without training you start taking a 1/3 penalty to further xp earned; make it 2/3 through and that penalty increases to 2/3.
Training takes a week or two, once you can find a trainer (exception: after about 9th level characters can self-train), and can't usually be done in the field as it requires access to facilities e.g. a lab for mages, a gym and sparring partners for fighters, etc.. It also costs a fair bit - rule-of-thumb is about 1000 g.p. per level being trained into, with a small random variance. If you've gone far enough into the new level to hit xp penalty, training costs come down a bit as you've already done some of it the hard way.
For the most part, the way I do it now (as outlined above) isn't really different at all from they way I did it in 1984 when I started DMing, other than I probably pay more attention to 'situational' xp now than I did back then.
