Thanks for the kick in the butt, Plaka. I shall get on with it. Checked with a magnet tonight when I got home - yep, it's steel alright. Good advice about marking the seal with a Sharpie to check for clearance - will try that tomorrow. Checked end play with existing washer - almost imperceptible and not measurable without a dial gauge, but it's there nonetheless.
I'm positive the inner thrust bearing is back on its pins, SS. Got it back on before I torqued or forced anything. Thing spins like a top with the flywheel back on (but without seal).
As always, grateful for the input.
One measly toaster