The mentioned Biopace chainring and crank arm set (refer to https://hackaday.io/page/10435-5-the-chainwheel-pt-1 ) were the next issue.

As mentioned also, the bottom bracket is a square taper model. The Shimano crank arms do have square taper also, but there are nice distinctions (refer 'ISO' vs. 'J.I.S'). To cut a long story short, the chainwheel took position on a wrong chainline, right of center, after mounting.

To bring it back to the middle there are four options:

1. To file out the square taper hole in the crank arm;
2. To choose another bottom bracket with JIS Sq. taper;
3. To choose another bottom bracket with narrower axle;
4. To shift the chainring.

For sure, #1 is a genuine hillbilly 'solution' that may ruin the crank arm. To be serious, it is a dead duck.
Also #2 or #3 bring up more work than wanted, remember my Waterloo with the BB mounting...

At last #4 will remain.

Chainring (with distance washers) at final position

With turning over (its inner side faces out) the chainwheel *and* bringíng it to the inner position at the crank arm the chainline is shifted to a reasonable position, finally. Also the chain itself is running well with this chainring.

Missing part: Covering plug for the crank arm bolts.