I used to tie a piece of line from the mast base to the striker post AND have someone restrain the mast base as I walked the mast up on my 5.O.
I also did the upgrade to new-style, and don't remember having to take out the striker bolts. The threads are a larger diameter on the post than the unthreaded portion, and the lower nut just spins down (and eventually off) the post as the post comes out the top of the beam. Be sure to read your directions about sealing the assembly, and also for prebend of the mainbeam. Have fun, and good luck!