Given that there will be several bolts through, are the toothed washers needed? As for driving, have a good pilot hole, if you cannot get a standard drill in then use the angle drill to get them in as far as possible without over stressing the drill and then use a socket and rachet to finish or one nearly in the standard drill may fit.
I did wonder about the toothed washers - esp. if I go the coach screw route which is looking increasingly likely. I'd read that they can be a pita to bite without a lot of clamping. Drilling-wise I'd also be worried about going off-centre as well. So I think coach screws is the way I'm going to go. Doubt my ryobi driver is up to task though! I do have a decent socket set so I'll follow the advice - thanks! The coach screws say they don't need a pilot hole but I'll do one anyway. What would to recommend for a 10mm screw - 6mm?