Folks: long time lurker (and dreamer) now a poster and hopefully builder.

I recently acquired a realatively traditional timberframe barn, 18x28 which came from near Lake Erie in Southern Ontario. It is a true homemade barn as no two timbers seem to be of the same species. My intent is to raise it as a workshop. Sheeathed in 4/4 t&g over a framed floor.

My quandry at this point is that cows, as a general rule, are short and thus the second level is hung at a mere 6 1/2 feet up the posts. If I want to use it as a workshop, I need to adjust it for my 6' body. My first thoughts were to simply place 6" or 8" sills under it to gain half a foot of height. Now, after re-reading all the resources on joinery, I am thinking of scarphing in an extension - I need to do this on one post that is too rotten to live with. I have seen this done in many books and web pages but never for more than one post at a time. Is it possible to use a stop-splayed, undersquinted and wedged scarphs to add height to all six posts or am I asking for trouble? The six main posts are currently 14' - will 18" - 24" make it completely unstable?

Thanks in advance

Scotty