Yeah I think 16/18mm for factory and 15mm/17mm for the BFI hardware, not 100% sure. I have a set of 8-19mm ratcheting wrenches from OEMTools and their metric passthrough socket set, which is a little lower-profile than most socket and ratchet setups. However, I still think that with a flex-head 3/8" ratchet you'll be alright, and I used a 6" extension for the bolts closer to the fender but I was able to move the plastic wire holder thing out of the way enough to gain access straight down.
Biggest thing when doing this job is to take your time, support the drivetrain (carefully, plastic oil pan), and be aware that if things are well-supported you should see the bolt heads rise from the mount, if they aren't rising nicely stop and reposition so you don't damage anything.