Whoa, interesting set up. I assume you are referring to the 16.5 Fairway Metal, with a shortened shaft of 1" less (16.5 is 43" and 18 is 42" standard lengths) you will need a heavier head weight plus some lead tape potentially.

I have not set this on the surefit setting to such a high loft but it will give you a similar length on the course as a 18. However, there are other factors that may not help you such as lie angle (moving ball in flight fade or draw), spin (higher or lower depending on what added loft you ultimately go with) plus a few other minor factors.

I feel, having done these experiments over the years, you are better off just purchasing an 18 if that is what you are going for. Since it is a smaller head it will allow you to escape bad lies easier than a 16.5 plus the 18 you can adjust with length and surefit settings for you game specifically.

IMHO

Also interested in this. Thinking about replacing my tsi2 18degree with a 16.5 and just swapping the heads out.

I have a TS3 16.5* fairway wood and love it. I am playing stock length and it's a fairway finder for sure.

Master Titleist fitter Glenn Mahler switched me from a 15 degree fairway to a 16.5 915F with one inch short shaft at a local fitting event, as it gave me better descent angle without much loss of distance. He also recommended a 21 degree fairway, vice a 21 degree hybrid for much the same reason. A few years later, another fitter put me into the TSi2 16..5, with a half inch short shaft. When Glenn fit me again at the TSR launch event at Carlsbad, he switched me to a 15 degree TSR2, vice the 16.5 TSi2, due to the higher flight characteristics of the TSR head, and again with one inch shorter shaft.

My next club is a 21 degree TSR 2, with a half inch short shaft. I have not experimented with an 18 degree, as I find this combination gives me appropriate gapping coverage.