Could use a serial number to make sure, but the Magnum doesn't have trim senders. The later version called the HP assembly used a single 3 wire trim and switch. It was used with digital gauges.
Mine is the HP and I have the single sender and also installed the Digital to Analog Merc converter, but it still doesn't work.
well poking around seems there are knurled press inserts- unfortunately just not for the 5/8 in marine stainless.. that would have been a real easy conversion! Hole is a few fractions less than 7/8..