Several thoughts.

1). 6-speed is more durable than 7 (126 vs 130 mm OLN), at least in theory. Some folks have problems, others do not. They shift the same.

2). 6-speed freewheels are easier to find than 7's. There is a guy on e-bay selling NOS Shimano 600 6-speeders in 13-32 and 14-34 combo's. I have bought several. I think they are running about $54.00 which is similar to the IRD, but they are better quality

3). I have gotten an Ultegra 6700 long-cage to swallow a 36T cog by running the B-screw all the way in. Sometimes this does not work, but 27T may not be the limit.

4). I have run wide chainrings and corn-cob freewheels for "alpine" gearing, but have frequently found myself having to run up and down chainrings as the middle of the normal power band splits the difference from 1-7 and 2-1. I think the 46-30 or what ever you are proposing would work better, but keep this in mind as you are setting up your gearing.