DCC Critical hits for S&W

I want to use DCC critical hits and fumbles for my Swords & Wizardry game. Fumble table maps directly. The classes map as follows:

Fighter --> Warrior
Cleric --> Cleric
Thief, Assassin, Monk --> Thief
Magic-user --> Wizard
Paladin, Ranger --> Dwarf
Druid --> Elf

The only thing I haven't decided is whether to keep the levels the same. DCC is only a 10 level game, S&W is theoretically 20. I think it might work fine to just keep the levels the same though. This fits with the flattening of the power curve after level 10. That being said it would be something to strive for at high levels.