6.0l valve cover removal
 

2005 E-Series, as in Econoline, E450 6.0, thomasbuilt schoolbus. 100% stock, aside from a zip tie here or there.
Poor drivability, low ICP pressure codes, and now a no start. Hpop only producing about 125psi at 87% Ipr. Ficm 12v in, 49.7v out, with sync.
Trying to perform air pressure test, but I can't get to the outboard center valve cover bolt on the driver's side. Already removed engine mounts on both sides and dropped engine down so the oil pan is sitting on the frame cross member. No matter how high or low I position the engine, there just isn't enough room to get to that last bolt. Don't have my crackerjack secret decoder ring or a shop manual. So is there something I'm missing, a trick to getting this valve cover off, like pulling the engine out? Like this isn't an in-frame operation?