I've got a few suggestions for you. First, I think the Monster Manual (or possibly the 2E Monstrous Manual, which should be close enough for this purpose) had tables and rules for equipping NPC parties with magic items based on the level of the NPC.
Another option is to let each player spend, say 10-15% (or maybe 1 - 1.5%) of their current XP level on magic items. You might prohibit certain items (No Deck of Many Things, or Rings of Wishes), or limit the PCs to items below a certain XP value.
Third, you can decide each PC starts out with, say 10 magic items, and they can decide how many are from which category (Ring, Wand/Staff/Rod, Weapons, Armor, and Misc Magic), and then you or they roll randomly to determine which type they are until they get useful items. Then give each of them 2-8 useful potions, and maybe a couple of scrolls (more for the wizards and priests, less for everyone else).
Disclaimer: I am completely unfamiliar with the H series, other than knowing they are for high-level characters.
Since AD&D gave xp for treasure, you could also allow the PCs to have any mundane gear they want (and can carry and/or transport), assuming that maybe 50% of their XP came from gold.