Following up:
I weighed many options based on time and cost. In the end I designed a piece that would adapt the mast section to fit the gooseneck. I brought the template and a scrap piece of 10 gauge 316 to a local sheet metal shop (that usually does
HVAC ducting) and had them bend it into shape for me.
The sheet metal cost me $20 and the bending cost me $80. I was being quoted between $600 - $1,200 to have a new gooseneck fabricated to fit my mast section...this solution made much more sense to me.
Anyone in the Bay Area that needs sheet metal
work done I recommend Metalmen Sheet Metal located in SF. For 316, check out Alan
Steel & Supply in Redwood City