Several things.....
Most crucial already mentioned - the oil pressure fitting on the engine.
If you are even remotely thinking of putting a cooling shroud around your fuel pump, do it with the engine off - its way easier to install the fuel pump with the engine off. You will need to be able to turn the engine over though. Lots of people don't think the fuel pump cooling shroud is necessary - and indeed even on some pretty hot days I have not had a problem. Still, its a simple thing that removes a potential problem, and it is cheap. It is just hard to install with the engine hung on the airplane.
Everything on the firewall is easier, but some things may need to wait for the engine mount or even the engine to decide on location, like the oil breather.
But Van's gives good enough guidance for the battery mount (if it is firewall mounted, which is most likely on a -7), control cable pass-throughs, starter relay and master relay, and the pressure sensor mount manifold. I have a double-row of adel clamps across the middle of the firewall that support the oil pressure line, the manifold pressure line, and a bundle of 2 CHT and 2 EGT thermocouples, alternator field wire, other wires, all bundled in a shrink-tube conduit to get them across to the other side of the engine from the side they came through the firewall.
I put my oil cooler on the firewall with a combination plenum/mount bracket, sort of like the RV-10 install, but made to fit the angles near my engine mount. I'm really happy with the firewall-mounted cooler.