You can try a flex socket and a long extension, or a combinations of different length extensions. What I do is loosen motor mounts and rear transmission support. This allows you to lower the transmission down a bit and get a little better accessibility to those bolts. Make sure everything is supported!
I've never had any problems getting them loose, but if they seem tight, I'd spray some PB blaster and let them set for a while. Use a 6 point socket.
I jacked the tail of the transmission up which tilted the motor forward enough to get my fat ass arm behind the motor from the top.... 13mm racheting wrench
Couldn't you remove the rear trans cross member and use a jack to lower it so the 2 bolts are at an angle and can be reached simply using a long extension?
^ I wonder if there is enough room for that on a dohc. Looks really tight back there (hehe). But that's a great idea.
Easiest way hands down is to pull the intake. Then it's any ratchet and socket you want. I can pull an intake in less than 30 minutes and the gaskets are reusable.
This is how I do it on Mustangs and F-series trucks. Pulling the intake is really easy and gives you a whole lot of room to work from the top.