I posted this, noticed there were four (!) more pages of discussion I'd somehow overlooked, deleted it... and am now posting it again.
How the Hackmaster "initiative" system is being described sounds fairly similar to my
Initiative Overhaul, so you may be able to take some inspiration from that. I have a greatly simplified revision I'll be posting on my blog once it's finished, so if what's linked makes your eyes bleed, you may want to wait for that.