The main oil outlet from the sump's filter body, is the one pointing to the right of the car, with a T-junction for the pressure gauge pipe. The main feed pipe then goes straight into the block to the main bearings. Full flow filters are inserted in place of this main feed pipe. On most installations I've seen, the 2 connections for the bypass filter were blanked off. On one engine, they had fitted a by-pass pipe, but I would have thought the lack of resistance, would cause too much oil to flow down it, instead of into the bearings.
Robin's AC Engine Project website describes a filter that incorporates a relief valve after the filter, to ensure that the correct supply pressure is maintained. This will need an extra pipe for surplus oil to return to the sump.
I haven't come across oil coolers on the 2 Litre, and am not sure if it would be needed?
There are plenty of electrical/electronic upgrades that one can consider: Electronic fuel pump, electronic control-box, and LED lamps including built-in flashing indicators.