For the Canadians, Performance World has their PW heads for SBM for $2249 CAD ($250 off) until the end of the day. They look identical to the Promaxx 171s but claim a 179cc intake / 79 cc exhaust versus Promax's 171 intake / 77 exhaust.
The PW's appear to be assembled with quality hardware such as PAC 1219 springs and Comp retainers and locators.