Good reading about your repair Andrew. One more SE lives.
I have a broken SE here
that defeated me. I've still got most of the parts (minus HD..I used that for something else) and if I ever get an SE junker with a working video board I might have another crack. I'm not too worried though as I've got an screamingly fast SE/30 which satisfies me.
One thing. I'm sure you know about this already but the standard old SC HD Setup doesn't recognise non-apple drives. This
caught me out when I was trying to delete At Ease from a Classic II. It was as if the HD just didn't exist! Even Norton's could only see it, it couldn't do anything with it. I was stumped unti I discovered the that it needed patching. Your drive obviously used to boot though so it likely it is stuffed. Is it an Apple-branded drive though? Anyway, just thought I'd mention it in case. You don't want to be throwing away a drive that might be salvagable.