From the MGM first letterbox LD onwards they’ve used 65mm elements.
The BD or any release is a good starting point but it mist be understood that unless you go with the Criterion, corrected MGM LDs or their DVD that there have been slight alterations to color and the sound mix. These are very slight to less so but 99% of people have no idea. It’s not quite as blatant as what happened to the other Warner owned Kubrick titles.
This isn’t to say that any release is perfect but at this stage with Barry Lyndon going to Criterion and not only fixing the aspect ratio, including mono but using the new scan more effectively-it is possible for 2001 to be done correctly.