As requested. I made this from scratch and there are no meaningful drawings. I followed the instructions in the manual to the extent I could, but they're not very comprehensive. It's constructed around 2 1/2 inch diameter 0.035 inch wall thickness 6061 Al from Aircraft Spruce. The assemblies are all temporary, so no locknuts etc. The filter is Part # BA 4310 from Brackett, and is the biggest I could find that would fit in the baffle plate. It's intended for an O-540 in a Ryan so should be OK for a four cylinder, although the calculations suggest it's marginal for 360 cu in. There are alternatives from K&N etc., but at least I know this one is tried and tested for aircraft applications. The cowl below the filter is four bid, formed over a foam plug.
It's one of many approaches I have seen, and in retrospect not obviously the most elegant solution, but hopefully better than workmanship of the week award material. One option is a cylindrical filter around the forward facing intake, with a butterfly that allows straight through unfiltered air or blocks the direct air and diverts it to the filter. That way you don't don't need to mess with the baffle plate.
Note that SCAT tube isn't recommended for engine intakes because it's not good with negative pressure and can shed into the engine. Anyone out there know of a good alternative?
Any questions, let me know.
Regards, Chris.