How to apply custom filters for John The Ripper when cracking RAR3 archive password?

My problem is that I’m trying to crack RAR file with is encrypted with RAR3 encryption.
Decided to try with John The Ripper.
Here are clues I have from my friend.

1. Max password length is 8
2. Only capital letters or digits

And I need now filter to make John crack the password without trying to check small lowercase letters.
On hashcat it’s easy to do but program do not support $RAR3$*1 type of hashes.