I'd bet on the open loop map is probably 13:1 out of the box at worst, with a target of somewhere around 14.7:1 under most light-medium throttle situations. You're not going to get your best mileage at 14.7:1, you'd need to be much leaner, like 16-17:1 for that. You can run that lean with no problems IF you're running light throttle and lots of advance. Unfortunately, that's not where the cat converters do their best work, and certain emissions (NOx, I think) go up. My understanding is that GM got hammered for this back in the 80's-90's because they programmed in a "highway mode" on their EFI systems, and although it got better mileage, it didn't meet EPA's req's. I think that's a shame, since you really have to be steady-state + light-throttle for a while to kick in to highway mode. That was also open-loop, but the computer would check back periodically by going back closed on some regular basis. I think this functionality is still in the GM codes, just disabled.
That's neither here nor there for Daty's setup. I think with a MAP giving a baseline baro every time you start up, air intake temp, and a known VE for the engine, you really don't NEED an O2 if you're not running cats.
