Just wondering what those in the know would think about putting a mast track in a 11ft or 11ft6 board , how would it compare to the naish 11ft6 with mast track ?

If you put a mast track in id suggest you re-inforce the box by laminating 10mm divinycell or klegicell around it which will help spread the load.

I do this with my fin boxes but only twice which makes the load spread across the whole surface area and also more area to get a good bond when glassing. Haven't had a problem.

I wouldn't be putting footstraps on it and trying to jump it or anything.

If you have a divinycell supplier near by they will probably have damaged sheets. You should be able to get some for nothing or very cheap. I haven't paid for any yet although I did by them a slab for their troubles.