Converted my beloved, seriously bastardised 20 year old Sunn Mustang P copy to active a while ago, wish I'd left if passive TBH - I scrimped on the circuit though, you get what you pay for!
Depending on your budget maybe it'd be better to just get a Sansamp BDDI and turn the blend 100% off, gives you a 2 band active circuit I believe? Saves chopping your bass up and you get a very versatile and cool sounding pedal too!