Placement of a wideband bung should have been thought about at the time of the exhaust design. Why was it not fitted? Can't blame the tuner here. Measurement of correct wideband A/f ratios are vital for your engine.  You don't have any true readings.  How will you get accurate A/F reading in the future when more aggressive tuning takes place?  Personally I would not tune a high performance engine without a wideband bung welded in.
 
I am trying to give you good advice.  Think about where you can fit a bung on your exhaust. Do it right
 

I am really hoping that this unnecessary tension between the two of is simply a technical miss understanding of technical terms. Your so called"2 O2 sensors" to me are what I and most people would refer to as standard oxygen sensors (they cannot measure A/F ratios), and not wideband sensors.  There is a big difference.  If you have TRUE wideband sensors at the exit of the three into one collectors then you would not need to sample A/F ratios at the tail pipe.  Question is why are you sampling A/F ratios at the tailpipe?
 
To simplfy my question.  Are your "2 O2" sensors Wideband sensors?
 
 

This is funny to read but anyway in my personal experience and from what I know B24 has nothing to worry about. It's a v6 engine and he has two O2 sensor bungs from the sound of it at the end of each exhaust header, which is a great place to have them from what I know. For my 6 throttle body 260z with a straight 6, I had a single bung at the end of my headers and this is where they plugged in a wide band O2 sensor to do the tuning. I didn't run a wideband permanently in the car, turner only ran it when tuning. My car ran without issues. They explained the reason they run it there and the reason one in the tail pipe is basically useless is because too much outside oxygen interferes with the reading from the tailpipe sensors on exhaust pulse, so as far up the exhaust system is better, plus the hotter the better. 
Also I don't understand why anyone building a race car engine would fit a non-wideband sensor in the exhaust let alone two? Who cares about fuel saving at idle and cruise speed in a race car? Seriously, it would make no sense for it to be a non-wideband. I understand if it was a factory engine modified, because who bothers removing it but a custom race engine, really?? 268RWKW in a NA MR2 sounds like plenty for track day fun, hardly going to tune it to an inch of its life to win a $20 trophy if that, just some good reliable power hopefully.

No worries Richard.
Neil spent time with me at Wakefield on Tuesday. We will be spending a day or two at the track sorting out the finer points of the tune. Will be data logging laps then working on it between sessions. 
 

kojab
Yes tuning it at the track is the best scenario to get the tune spot on, far superior than any dyno and safer for the engine too.  That's my opinion anyway and I have been tuning this way for last 30 years. Now retired. 
 
What was your best lap time at Wakefield with the current tune?

I expected to have the car run in then tuned to the point that it can be taken to the track for more development. Always had Neil in mind for this part of it. 
It did a 1:07.7 which is a good start. There is more time in it as it has no real development, brake bias was badly out, tyres old and worn, me fresh in the car. 
Aiming for 1:05's by late next year. 

Steve, yours is an unopened engine right? All mods were exterior?

B24
I expected to have the car run in then tuned to the point that it can be taken to the track for more development. Always had Neil in mind for this part of it. 
It did a 1:07.7 which is a good start. There is more time in it as it has no real development, brake bias was badly out, tyres old and worn, me fresh in the car. 
Aiming for 1:05's by late next year. 

If that's Motec Neil then you have no worries getting the tune right.
I would say 1:07.7 is a great start.