Hey Dave, I've run turbo motors in all three configurations:
740-style with an arm off the blockSandwich plate right on the blockNo oil cooler
Currently I don't run an oil cooler and after 18 months of it honestly I haven't had any issues with temps, oil getting burned or anything like that, but the car only runs 10psi. I do like to thrash it occasionally, and I change the oil about every 5000km.
The 740 extension arm I would avoid, it's a real nuisance for routing the oil hoses. A sandwich plate on the block is less work and leaves a bit more clearance for your downpipe. The main issue is getting the oil lines around the steering column safely. I had one get caught by the knuckle once and it dumped oil all over the carpark floor in Broadway shopping centre, lots of fun.
If I were going to add an oil cooler today, I think I would mount the oil cooler between the condenser and radiator, on the rad support panel, bend up hardlines with AN fittings and run them from the oil cooler down the driver's chassis rail, then run a braided line from the chassis rail to the block. You could also do this with soft lines but just make sure you make liberal use of P-clips.
If you do want to run a sandwich plate off the block and require an extended oil filter thread, the filter thread is 3/4"-16 here's one on eBay. Finally, if you want to remove your oil filter thread without destroying the thread, use a thread extractor down the inside of it, works great.
