Welcome to AO Tom.
You've got to post some pics of your Delta, such an awesome motor
As for the 166 wheels, those shown are Alfa originals (17" I think and probably the nicest the 166 came with) so either a main dealer or trawling ads/ebay etc would be your best bet.
GTA wheels, from what I've read, aren't the best quality...although I've no personal experience of them.
Welcome to AO Tom
I've got an accesories brochure and sales brochure for the series one 166 which i've just looked through but they dont seem to list them anywhere . The sales brochure shows a lot of pictures of the 166 fitted with the alloys your looking at but no name for them. Sorry I cant help you on that one but someone else on here may know.