The D2 heatshield has a large spring clip that locates over the starter solenoid, and a small 8mm head screw that goes through the web of the engine mount on that side.
X 2 on disconnecting the battery!
I used a long 3/8" drive extension to get in there to undo the bolts, it isn't that they are cap heads that causes the problem, it'd just their location.
Peter