I found a couple of standard, over the (Autozone) counter, bulbs that worked in my '91 Olds and may work for some of you. I say "may work" because I'm no sure if these bulbs will effect cars with the bulb detection ding-ding. But, I believe, most owners of 87-91 H-bodies should not have a prob.
I replaced the Stop/Turn signal bulbs from 2057 to 3496. It was interesting to find that the OE bulb behind the amber front turn signal lens was a 2057NA(Natural Amber) bulb. Why they put an NA bulb behind an Amber lens is anyones guess. Anyway, the 3496 bulbs made a dramatic difference in brightness for both in the parking light mode and the stop/turn signal operation.
I put a 3497 in the CHMSL.
I replaced the the 194 front/side marker bulbs with 3652 bulbs. Once again when I replaced the bulbs that were behind the amber lens up front I found the amber 194NA bulbs. Anyway, this upgrade made noticeable difference without affecting the turn signal flasher unit.
These bulbs will probably not last as long as the OE bulbs. But, after over 13 years of service, almost ALL of my bulbs were OE! so if they last only 5 or 6 years instead of over 13years, that'* OK with me.
L.E.D.'*? We don't need no stink'n L.E.D.'*!!!