Running Four O2 Sensors ???

This is a if you could how would you build it question/discussion. If you wanted to build a header to run one O2 sensor per cylinder and had no restrictions on space how would you design it. What tube diameter, O2 location, How long should the tube be from the sensor to the collector to prevent backflow from generating bad O2 readings. Looking at building or having a turbo header built. This started with my brother wanting to turbo his legend car for autocross racing. It got me looking at changes on my planned build.

Alan Jones had 4 O2 sensors on his red glhs. The tube diameter and such depends on head porting and turbo size in my opinion. But there are a handful or 2 of guys with tube headers

A few people have done it. No restrictions on space is kind of hard to imagine, as space restrictions are probably the foremost reason why so few people have done it.

The no space restriction is due to no longer being FWD. Header building is one of those magic arts I am wanting to learn.