what is the differenct between the stock udp and the aftermarket one
About 9 pounds and an inch.

Stock UDP (can be bought in a group buy right now)
And.. about the underdrive/overdrive pulleys..... because of the lack of aftermarket for our cars.. there is no set we can get... other vehicles with more aftermarket have whole pulley sets available. UDP (crank), ODP (alternator), ODP (power steering).. and they are all lighter weight.
how much do they cost in the group buy