Ian,
My DRB from Australia was not built there and was completely stripped of the previous owners attempt at building, converted to Left hand drive and many under finished parts replaced with parts that would standup to racing needs. The battery is in the front compartment in front of the passenger seat.
Oil requirements included a remote placement of the oil filter to the drivers side above the axel and bolted to the trans housing. The fixture that holds the oil filter is one with 4 ports, of entry(2) and exit(2). This gave me places for the lines to the oil filter and back to the engine, courtesy of an adapter on the engine where the filter was originally. The other two ports afforded me, one, a direct line to the oil pressure gauge(actually an in line but it is not flow directed so it works perfectly for the pressure gauges). This line was divided to a second pressure gauge that was wired into the fuel pump wiring(more on that later). The outlet from the filter, before returning to the engine was plumed to a thermostat that on startup, returns oil to the engine. As it warms up it diverts the oil flow to a cooler that sits in the left body opening at the rear. This radiator has a puller fan mounted between the cooler and the stainless steel wire mesh that was placed on the outside of the body panel opening with a retaining cover. The second out port of the filter housing has a thermostat that would turn on the fan automatically. The fan at the cooler is also controlled by a switch at the dash . The switch is for backup in case the thermostat jams or becomes inoperative.
I also run an oil accumulator that holds 3 quarts of oil under a pressure of 50 lbs. The line from and to the accumulator is T'd into the return line to the engine. The return line must have a one way valve in the return line, after the thermostat and before the Accumulator line, . This is for when the oil from the acumulator is triggered. It makes sure oil isn't pumped backwards into the cooler.
The accumulator can be wired in two ways. It can be activated with the ignition switch so that when the key is turned to the run position, it will pre prime the engine with oil prior to starting. Probably better for an engine that has been sitting for some time and avoids a dry startup. The accumulator can also be wired to an oil pressure gauge so that if the oil pressure drops to under say 30 lbs., it will trigger the accumulator to pump the 3 quarts of oil into the engine to maintain pressure. Sometimes this is due to high G forces on the oil in turns which causes it to walk up the side walls in the oil pan, or the pickup rises out of the oil. Usually not a problem if the oil pan is baffled(think roll over). When the oil pressure returns to above 30lbs.(my oil pressure runs between 45-50lbs.), the extra oil is returned passively to the accumulator. If the oil pressure does not respond to the extra oil and falls to say 20 lbs. then the electrical system shuts the fuel pumps off in an attempt to save the engine(think roll over), or what is left of it(non rollover). The switch with the variables can be ordered at the time of purchase.
I have a AC compressor mounted on the drivers side of the motor but have not plumbed it into the car as I wanted to see if I really needed it. I don't. It is well insulated and air flow through the radiator is ducted to the twin nostrils and very little reaches the front firewall.
I added one other safety feature to my oil pressure setup. Instead of the wiring going to the ignition switch for pre priming of the engine(for startup), I have it wired to an on/off push button that acts like a bypass switch, so that when the fuel pressure pumps are turned on at the dash, prior to starting, they will run. Now remember, that If there is no oil pressure, they won't turn on(unless the bypass button is pressed) and for me that is a safety feature if someone attempts to steal/start the car.
I had a concern about only having one bay filled at the rear(oil cooler), so I plumbed the second bay with a second cooler for the trans. I have a 930 transaxel and the engineers say it is unneeded even in a racing scenario, but I wanted to even out the look, So it is wired with only a thermostat.
Bill