Thanks to your advice I have made good progress today.
Craig - You were right. I rang Peter Sansom today and spoke to Melinda, who suggested I ring back at 5.00pm when Peter had some quiet time. I did and found him to be very helpful. He even has records of when my body/chassis was built and the agent it was sold through. Basically my only option in NSW is the LS1. He assures me it will fit, and gave me contact details for a DRB customer in the Blue Mountains who has recently registered an early chassis like mine with an LS1. (Sounds like Ben's mate.)
Front cross member already has a big notch, needed it to clear the Windsor also.
Ben - I spoke to Peter Smith (Engineer at Camden) no problems doing the DRB with an LS1. Also spoke to Jeff Bryant. Seems a "No nonsense" sort of bloke. Basically told me to stop worrying about things that weren't really problems and get on with it. He can fit the LS1 and get it running, and do anything else I can't/don't want to do myself. He is very confident we can get the car registered through Peter Smith, who he has used before and is happy to use again. Also told me to rejoin the NSW Cobra Club and ask for help, instead of trying to do it all by myself and worrying about things other people knew how to do.
Thanks again guys, I will keep you posted on progress
Regards
Garry