The main girdle was probably the most fun and straightforward part of the bottom end. I milled it out from a solid blanchard ground steel. I didn't feel like messing around with some shim arrangement so I milled the tops of the main caps flush with the bolt holes and measured the distance between them and the girdle. Aluminum "cap straps" were made in that dimension fitted per cap to act as the spacer between cap and girdle. I feel that these would still give some of the benefits of a an aluminum cap and still be as stable as an iron cap. I think it worked quite well. J.Rob