Al, relax a little. That is the Bergmann shroud you're talking about. The one Martin has uses an actual Porsche 11-blade fan and alternator. I wouldn't buy anything from Bergmann. Nothing at all.
A 911 axial fan is a completely different animal from a hamster wheel 356/Beetle fan.
Martin, I have that same hunk of aluminum base for the ring. Mine has a stainless steel strap to hold the ring, it works fine. Really easy to line up the pulleys too. I'm running a 5" dry sump pulley and a stock 911 alternator pulley. The pulley ratio is fine.
I have the same setup as Martin. I took a later year(mid-70s) plastic tailcone/vane assembly and modified it a bit. It bolts to the back of the alternator. It has two steel vanes riveted to the plastic cone on the 3-4 side of the engine. These require trimming to clear the shorter shroud. I also bent them a bit to force the air toward #4 as much as possible. The key is to also seal as much as possible between the fan and shroud and top and sides of the case to remove all the air leaks. I used foam window weather-stripping in various thicknesses, the kind with peel and stick adhesive on one side. I also made my own sled tins from aluminum sheet, tucking them behind the fiberglass and bending a smooth radius then keeping parallel to the case edge, with the opening to the rear. I cut holes for my J-tubes to pass through.
The sealing and modified vanes keep the CHT within 10-15 degrees Fahrenheit of each other. The sled tins lowered the CHT a further 10 degrees across the board. If you seal the edges from leaks, you then create even pressure across the cylinders and heads. The whole thing works like a forced air plenum. There is plenty of pressure too, the fan can cool 6 cylinders.
I had monitored the CHT with 4 separate thermocouples, one on each head just next to the spark plug. I drilled a small hole and threaded a 6mm bolt into the heads and used ring-style K-type thermocouples. It's the way Aerovee(which are for homebuilt VW-powered aircraft) engines monitor their temps. I fact that's where I purchased the thermocouples.
I have a crossbar/hexbar linkage, but I don't know if that will work in a Speedster. The twist pullrod linkage should work fine as long as there's no slop.