The flywheel was designed specifically for use with a '93 - '97 Ford Ranger 4.0L clutch and pressure plate. The Ford happens to have the same number of splines and input shaft diameter as the F40 transmission, and best of all, the other measurements all work as well. I decided to opt for a clutch package from SPEC choosing their Stage 4+ full-faced carbon-graphite-semi-metallic solid-hub disc with 778 lbft torque capacity after being reassured by my flywheel-designer friend that its street manners were quite acceptable. He's got about 12K miles on his LS4-engined Fiero. The Northstar generates 300 lbft of torque so it should hold without any slippage.
I ordered up the clutch (part number SF964F) from Canadian distributor "Steeda" in Ontario, which sells performance Ford parts. The part number isn't listed on Spec's website but it is available. It was especially painful for the pocketbook coming in at $778 after taxes and shipping.
Here's the business side of the pressure plate:
It's the biggest diameter clutch that physically fits inside the F40 bell housing. The clamping surface measures just shy of 10" at 9-15/16".
The pressure plate alone weighs in at 11.62 lbs which is within a half pound of the stock Fiero pressure plate for comparison's sake:
Here's the solid hub clutch disk... note that the full faced friction surface helps driveability significantly over the various multi-puck designs available on the Stage 4 disks:
It measures 9-27/32" in diameter so it's 13/32" smaller than the wear plate on the flywheel and 3/32" smaller than the pressure plate clamping surface:
The other unique feature of this clutch disk is that the splined hub is entirely offset towards the transmission side. It's deep too giving 15/16" spline engagement:
The clutch disk weighs 4.92 lbs so in all, the flywheel, pressure plate, and disk weigh 29.24 lbs total.
Compared to the stock V6 Fiero assembly weighing 30.6 lbs, I'd say the Northstar design is pretty darned good. The same assembly off an LS1 engine weighs a whopping 56 lbs!
I took a photo of the disk mocked up on the flywheel to show the relationship between the edges of the two parts:
And here are all three parts just mocked up on top of each other: