Coisox, C64 has answered if for you with his question. Thats basically how I would do it.
See his code chunkk and my reply to him below for how to make it work.

VIC20 C64 your answer is if(is(you,FLAG6))

A collision is two objects colliding, one is "me" the other is "you".
In the case of EVENT_BLOCK, "you" is going to be the block that 'me' ran into...