Yes which 87 matters. 30 is common to either 87 or 87a when relay is in one of 2 states, energized or not energized ( and I can never recall which is which. Refer to relay schematics ).
The current required to energize the relay isn't a substantial additional load on the blue switched hot, but at the same time... That switched blue was barely adequate for the OEM load in a 69 model.
If you're adding electronic ignition, etc... you should consider a relay in that current path. Thus less current drawn through that 69 ignition switch.