The Steelhead Plus did take a .350. No problem installing a .335 shaft, but we would use the LE9002 plastic sleeve with attached ferrule which is designed for inserting a .335 shaft in a .350 bore. If the shaft won’t go through the bottom, and I checked with Jim our resident expert on all things repair, the bore is not cleaned out completely. When we have our repair schools, we actually used the Steelheads in the class for a time to demonstrate how to re-shaft bore throughs, so Jim has done it literally hundreds of times. Unless something was done after the original assembly, there should not be any obstruction once the old shaft is removed and the bore has been drilled/cleaned out through the entire bore.