Originally Posted by
Decadence
A recent roadie resto-project of mine came with an exage/biopace crankset, and while I haven't been up any steep hills yet, the biopace rings feel good and shift smoothly. They probably aren't super-light but they're totally functional
If they're ally forget the weight, NBD. But a plain big just doesn't cut it next to one with ramps and pins, especially if it's properly indexed to the small ring, and Shimano (I use SRAM rings on one bike because ramps and pins by anyone is way better than none, the rest is diminishing returns). The Biopace big rings are pretty close to round, anyway; they don't do much.
To index a modern big ring against a Biopace small ring, you'd need to have a matching small ring to find a position to mount the big ring so the small ring's teeth are in the same spot relative to it. Since it won't be a 40t, you should be able to get it close enough.