Always good to have more info. I'm not sure that the ports grc are displaying as stealthed is the same as the ping port - I think you'll find the former is a TCP/IP ports list whilst the latter is an ICMP port. I'm not a networking guru, so I'm not sure what the distinction really MEANS.
Edit: You got another post in before I submitted!
Yes, enable the block. I would be surprised if this didnt do it - why would you want to be pinged from the WAN (read internet) after all.