Many thanks for your support! Meanwhile I studied Paulo's track building tutorial part 1 and part 2. Unfortunately I didn't find part 3 he announced at the end of part2 but apparently didn't publish. So I think you're right.
Still I don't know how to import objects from another track into GP4Builder but obviously haven't studied the User guide carefully enough...
Anyway, Atticus' Road Atlanta is a track worthwile to invest some effort into evaluating it with some environment.
So any help for that project is more than welcome for a track building novice as I am.