If you want a Bj4 your better off getting a B44, basically same car but parts availability is much much better as almost nowhere stocks bj4 parts now...
There are no conversions for bj4 to b44 vice versa etc
As others have said if you can try several peoples cars if they let you before you decide to buy as you could much prefer one car to many others.
Regarding the X6 non squared theres usually one in the forsale section I think someone is selling a conversion with few bits forsale now, otherwise ring dms-racing and they will let you know if they have any of the non-squared kits still.