906's cost $60-100 a pair. 915's several hundred a pair & are fairly hard to come by as it was (1)year only(1967) whereas 906's ~ 3 years. If you want a quench motor(smart move) & dont want to step up to one of the alum heads then go with a 915 with the right piston/head gasket.

live every 24 hour block of time like it's your last day on earth