Different size torque converter knob 170 vs 225?!? Are you kidding me?

The custom torque converter (splines for '68-up input shaft, nose for '67-down crank) is a sure-fire way forward, shouldn't be too costly, and as Redfish notes, it's compatible with either type of crankshaft (just add an easily, cheaply available spacer ring if using it with '68-up crank).