Made some advances with the helicopters today.
The Chinook is built from the helipad as it should be
Longbows/Hinds work like Longbows/Hinds/Orcas now rather than like the RA2 Harriers (you can land them, you can have more than one per helipad, etc).
Also, the Mobile Gap Generator is in.
It can't be replicated properly but it I've got a workaround and I'm putting it in for the sake of completeness.