I just got an email response from Hamilton Bowen on this project. He has converted plenty of SP101s from .32 H&R Magnum to .327 Federal Magnum without problem. As should be expected, he suggested that it would need some some additional work to go along with the rechambering. I'd probably want some upgrades to the sights and action anyway. The problem is that they have too much "non-catalog work" right now to take on new special projects and that's exactly what the underlug modifications would be.
As soon as I got Mr. Bowen's response, I sent out feelers to track down a good-condition 4" .32 mag SP101. Do any of you have comments or recommendations?