I don't think triplizing the 151 is such a great idea. What's the point? It will significantly decrease in both monetary value and authenticity. If you're after utility, there are other cranks that offer lower gears and have the option of a granny gear.
I could be wrong, but I don't think a 1961 Record Strada crankset in well used condition is worth enough that I need to worry. I looked on eBay and seems you can pick up ones nicer than mine for $100 or so?