The lugs for an aluminum wheel vs. a steel wheel are VERY different. The tapered lug that holds a steel wheel on normally has no shank, lugs for an Aluminum wheel require a shank, or they will compress the soft aluminum to the point that the wheel will become unsafe/unusable. I would take one of the old lugs to the parts store for thread size match, and look at the lugs for aluminum wheels. You will want to measure the thickness of the wheel to be sure to get ones the correct length. They will need to compress a little. Some of the older mag wheels used a washer between the wheel and the lug, I believe yours do not require it. If you have an Airstream dealer nearby they should be able to tell you what you need, or possibly have them on the shelf.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato