I love the old bimmers, and your right, the alpina 2002's are getting bloody expensive, id love to get a 2002 (probably not an alpina, i doubt ill ever afford one of them), and
modify it, as much as i like them, and as much as people would look at me with disgust, its just something i do, and find it more entertaining to shoehorn a motor much larger than the capacity of the original, into an engine bay that was never designed to have an engine of that size in it, and go from there!
Make sure someone is taking pics of the rally when you get it there! or a video, would be great to see, wish more of my mates had land that i could do that sort of thing on, and i wish i had the funds to have as many cars as you!
Good luck and keep us posted!
Doc