the terrible sound of big end knocking or something else

[redrover]

I think lightweight doors would be a good start !! Anyone who has removed a door and carried it away can testify that this is most of the weight !!

I know what you mean! I nearly herniated taking the back doors off mine! I think the mechanisms contained within are contributing the real killer weight. God knows what they must be like on a NADA!
If you stripped them out and fitted sliding perspex windows and a simple pull-cord door release acting directly on the lock mechanism, you'd probably end up with something 30-40% lighter than standard. An aluminium door skin if you were so inclined would also help matters, but probably not a significant enough weight loss to justify the hardship.
In either case, you'd retain the door carcass and its inherent strength, which would be a big plus point for me from a safety perspective. Not just in terms of impact resistance, but also in preventing them from flying open in a bend due to poor panel gap. Anybody who's pressed a less than perfect Herald convertible round a fast corner recently will know how bloody scary that can be!

Michael