[Canuck]

Good points on all counts. It would appear that the two cars chosen to pace the INdy 500 are performance models,to the extent that the actual pace cars got tweaked to do the job> this became more a necessity in the 70,s as the off the shelf performance packages were not up to the standards to get the job done.
Case in point was the 72 Hurst Olds. The actual pace cars got modified 455's, special gearing and bigger brakes. They did not use the "X" code 455, but rather built a special engine with mostly 1970 components.
In 1964 the Mustang,as a pace car was a convert,but Hardtop models with the less potent 260 were used for parade duties.
In 1973 the Cadillac had to be modified by stripping out 500 lbs of weight and seriously tweaking the 500 cu in engine to meet the requirements.
I see the selection of the 1970 442 as a choice of a performance convertible, interesting that no 442 hardtops were offered as pace cars, yet the Cutlass Supreme converible was.
Looks like each manufacture opted to celebrate their involvement in different ways.

Paul