1) A major consideration of the FWF design is oil cooler placement. The oil cooler selected is a variation on the Niagra 20002 style recommended for Corvair flight engines. The specific type purchased is the Airflow Systems 2002-X, an Experimental Only oil cooler design that is intended to provide superior cooling to the FAA approved variations. It seems to be popular with the Van's crowd so that is a reasonable endorsement. It is not the cheapest, but it is not the most expensive either and was used by Mark Langford on his well known Corvair powered KR-2S aircraft.
2) One option for oil cooler mounting is horizontal against the firewall. With this variation the air is ducted into the top via a 3"" SCAT hose from the aft right cooling baffle. The exhaust exits from the bottom and mixes with engine cooling air on the way out of the cowling. The only real issue in this orientation is how to route the SCAT hose. It can possibly come straight in through the top using a custom fiberglass duct fairing or it can come into the side which requires a 90 degree turn in the inlet duct. While it is not all that obvious in the photo that upper brace from the engine mount makes it a difficult fit so the cooler has to be kept low but then the lower brace becomes an issue. In the photo the cooler mounting flange is actuall in contact with that lower brace to maximize clearance for the top inlet duct.
3) Examining options that can avoid the fit problems with the horizontal mount I thought of a vertical mount that exits the heated air out through the cowling side in a louvered section. That makes it easier to route the inlet ducting and the inflow would come straight from the SCAT tube. The potential downside would be getting enough outlet area and avoiding a high pressurer on the outside that would minimize airflow.