What index will my 72 be in?

Glad to help. But 2 things I'd like to be sure you're aware of:

1) The horsepower ratings used to determine the class based on the sanctioning body posted shipping weights are the numbers "assigned" to the particular engine you have, not the "advertised" #.

2) When you determine your particular class in Crate Motor Stock, it has to be able to run at least as fast as the index for the class. In other words, the index is a minimum performance requirement. If you are faster than the index, you can dial faster. If you can't run the index, you will be dialed-in at the index, not any slower.

Good luck!