If you haven't made arrangements already, I can't recommend Dennis Booth of O.N. Booth & Co highly enough. He's in Ashfield, which might be a bit less distance to travel if you're worried about doing any more damage. It's really hard to help diagnose here of course, but what the NRMA guy said must be a bit worrying for you. Of course, it's altogether possible that he doesn't know diddly about older cars....
Dennis' number is 9798 8521, and he's on Frederick Street, opposite Wormald (250m or so up the road from the start of Georges River Road, heading towards Canterbury). What Dennis doesn't know about old Holdens isn't worth knowing
He's a one-man show, and it's possible he's on holidays at the moment, of course.
Hope that's some help to you.
Oh, and for what it's worth having a grey motor in the car doesn't necessarily mean it's the original one ex-factory. If it is, then there is definitely something to be said for getting it reconditioned (if that turns out to be required). But if it's not, then it makes no difference whether you buy another ready-to-go grey or reco the one you have.
Going from grey to something else is an entirely different story, of course.
cheers
RET