Thanks for you input Chris.
Your description confirms the dilemma that I have faced and since I have the standard seats, I am limited to about a 20mm space on each side of the drivers seat to fit my attachment points. There is a little bit more room on the passenger side but it is still fairly tight. As you have already experienced, I am in the process of fabricating customized brackets which will allow for the required attachment points to fit in the space available and the extra height should alleviate the issue of the adjustment buckle position as you have mentioned. I have also incorporated the attachment point for the lap/sash belt onto this bracket arrangement which should keep thing fairly tidy.
Sorry for hijacking your thread Ian.