Assuming this isn't something that you need to have right this second, stay on the look out for used MFC Mark IIIs. I've seen them out there. Buy one when you feel you've gotten a good price. Then sell the MFC Mark I at the price you can get. If you are patient, you'll buy and sell at a good price. I was patient buying an MFC Mark I and got it for $460 shipped .. plus it came with magnetic labels that I turned around and sold for $25.
I'd do that before modding the Mark I. At best, you spend more in time and money to get it done, at worst you hear yourself say "oops" while the solder is flowing. Having a stock Mark I to sell is preferable to having a broken Mark I to sell.
Time is such a big factor. If it takes 15 minutes to carefully replace each switch, that's over 5 hours, not counting prep, problems and testing. Makes the math hard to work out. Taking shipping out of the equation and a new Mark III = $750. Sell used Mark I = $500. That's $250 to pony up. If you can't budget $250, them maybe with patience you get a used Mark III for $650. $150 to pony up. Now use that $150 instead to buy parts. Maybe the parts run $100. You've saved $50 before even getting into the 5 hours of time spent and system down time, and at greater risk.
But, if you dare, and you get the switches changed out for under $100, I'm sure people will want to know how.
