RE: Which ICU for 45 IRS
"Either plug" will not fit. Only the R6F type will do because it has a taper seat, just like the champion RDJ6J plug
The R6A type plug has a flat seat, and is not a direct replacement alternative.
The Vlach-ICU replacement has the same plug boot like the old Vlach it replaces. It also has the timing to suit the Vlach magnet/sensor position