Well, if the oil was REALLY dirty, more than likely it was old and "worn out" too. Probably lost a lot of its lubricity.
As far as where the oil filter is, i dont believe those old twins had one.
At least not a spin on, or cartridge type filter anyway.
Many old Honda's used a small square screen type filter that the side case of the engine needs to be removed to get at.
Best thing to do, is (if your lazy like me) just keep fresh oil in there (every 500 or so miles) and clean it once a year. Depending on how many miles you put on it of course.
Might want to check -w- your manual or friendly neiborhood Honda dealer. :)