Lead fuel additive is available at all of the larger service stations and speed shops, you pour one container in to your tank each time you fill up full. Leaded fuel is a thing of the past.
Remember that humidity is very high here, if I was considering a prized classic car to be imported to HK, I probably wouldnt do it, best to leave classics in a nice dry country, where cars can be properly garaged, not left in damp underground car parks, or worse still left outside for the rats to systematically chew at all the rubber/foam components.
I do however, know of a 60 year old British man who specialises in pre 70's car service and restoration, he lives in the Sai Kung district... The only person I would ever get to work on one of my vehicles is him.
If you have the right people to help maintain your car ( very rare in HK ) and if you can properly house your vehicle from the humidity ( near impossible ), you will be tear free.