This isn't meant to sound rude but I am afraid it might come across as such. Here goes anyway- why? Why would you want to convert your mast at all? If you want a deck stepped mast, buy a boat with that feature. If you prefer keel stepped, then go with that from the beginning.
I just remember looking at so many boats prior to purchase
that had owner modifications that really left me scratching my head. If you are buying
a boat, I would hope you've done some research
into the design and designer
. If you like a boat enough to buy it, you should trust that the designer
used his/her best judgement as to the best type of structure for that particular design. If you don't trust the designers judgement, buy a different boat!