Cool...
The tactical/initiative system in RMC is relatively simple.
Initiative = roll 2d10 + Quickness Bonus + Mods
And resolution is handled (basically -- this is slightly simplified) using the following steps
1) Declare actions (and activity percentages) for the round.
2) Roll initiative
3A) Resolve short actions (actions of less than 50% activity) in initiative order (from highest to lowest)
3B) Resolve the rest of the actions in init order
4) Upkeep (i.e. this is where bleeding is counted, where stuns are removed from the total, etc.)
Most of the activity percentages for RMSS Arms Law system should be roughly the same (instantaneous spells are 75% activity - 10% casting, 65% rmandatory recovery -- that is something that might be different), and so should work ok.
If you happen to have RMX (you can get the PDF for only $5 from ICE's online store), it would give you a basic version of the system.