RMD,
The following option parts are worth considering as well
VZW206-18 Aluminum Pulley(RRR/18T/1pc)
VZW206-21 Aluminum Pulley(RRR/21T/1pc)
VZW206-23 Aluminium Pulley(RRR/23T/1pc)
VZW206-24 Aluminum Pulley(RRR/24T/1pc)
VZW206-27 Aluminum Pulley(RRR/27T/1pc)
Especially the 21T for the mainshaft as the plastic pulley wears fairly quickly.