Both the ensign spars and bristol bronze parts appear to be equally strong. The cross-sections and alloy choices appear similar. The failure modes for my tiller were dissimilar metals (prior owner installed an aluminum tiller in the bronze casting... Not good) and wear on the bolt holes in the tiller head casting. If you have the original and the holes a just a bit oblong, you might want to talk to a welder experienced in repairing bronze (a propeller shop can fill the holes back in and re-machine the part)

I'm not concerned the original part is "under-sized" 40+ years of service is a lot to ask. My project this year is to replace my tiller head casting with an original pattern part. The rough casting is on the workbench awaiting a keyway and some time in the drill press.