Hi everyone! Following the advice of other forum members, I was easily & quickly able to get Delta to comp me Gold Medallion status (based on my UA 1P status). I FAXed my request to the general Delta SkyMiles service center (404-773-1945) on Tuesday, and they had updated my status by Friday!
I just made 1P on UA within the last month, so I didn't have a 1P card or printed statement to send in... but no matter. I included just my request and a printout of my YTD flights from united.com, and Delta seems to have been fine with just that.
Happy flying!