Rotor cranks

Yep, agree with all that. I don't see how it's "kind of" though?

i.e. Dan has 3DF cranks, which are BB30.

He needs a BSA to BB30 bottom bracket to use them on his BSA frame.

A BB30 to BSA converter won't be any use to him.

I was just picking holes - self inflicted joblessness has turned me into an internet bore.

You can't convert a BSA frame to BB30 which is fortunate as 3DF cranks aren't BB30 - they just happen to have a 30mm spindle. Like S950 and Vuma Quad.

Adding the Rotor BSA30 just allows you to use these 'long spindled' 30mm cranks.

It might work with an inverse shim.

The 3mm ones are as rare as hens teeth. And you'd need two.