Bulbs are generally sold by style/fit. With the advances in technology, there are many manufacturers making older bulbs styles with new technology.
The stock 89 headlight bulb, as croat1 and Red89 have pointed out, is designated as an H4 Bulb.
Since technology has changed, so has terminology. The old style bulbs at 55W probably put out about 1000 lumens, but today's LED bulbs are capable of twice the light output and only half the power. (2000 lumens, 27 watts). With the difference in terminology, it can be difficult to compare.
But the thing that DOESN'T change is the H4 designation. All H4 bulbs should fit the same, so just do a search for H4 bulbs and you should be able to figure out the rest.