I am qualifying the following by pointing out that the following is based on early models with 25/36 primary and 32/70 secondary drive ratios and five speed transmissions, not a later model with perhaps different primary/secondary drive ratios and six speed transmissions. However, I believe the logic applies to the OPs situation.
Dropping 2" in rear tire diameter has increased cruise rpms by about 250 with a 30/70 secondary drive setup. I suspect you now want to lose the increase in cruise rpms by changing that secondary drive ratio? Just a couple of things to consider before making a decision.
Changing the trans pulley to a 32T will reduce the 250rpm increase to a 50rpm increase therer could be problems with the drive belt not being able to accommodate the extra two teeth. The axle will have to moved about .56" to accommodate the 32T pulley so, if you have that much adjustment, the drive belt might work. If not, you not only pay for the pulley but you have to buy a new belt.
You could buy two pulleys, a 32T for the trans and a 68T for the wheel and the stock belt should bit OK. There is a 68T Sportster pullley that some have used to make this conversion. The 32/68 secondary drive ratio will put your cruise rpms about 50rpm less that your cruise rpms before the tire change.
You have to remember that any secondary drive ratio change is going to affect rpms in every gear not just 6th. Additionally, even if you do the work yourself, the cost of pulley(s) and maybe a belt will be more than replacing the new rear tire with the stock Dunlop that is 25.63" in diameter, or the tire of your choosing as long as it is 25.6" in diameter.
JMHO, but consider replacing the new rear tire and selling it to a buddy.
