[DonC]

Mel:
Went round and round with Chris about the placement of the O2 sensor. He (the instructions) call for it to be mounted within 18" of the manifold/exhaust port. Given the primary pipes are in the neighborhood of 30" long I wanted to mount in the collector but Chris was adamant about the max of 18". As a result mine are mounted in the #1 and #5 primary pipes about 13" from the head. I had to port the driver side heat shield to clear the top of the sensor on that side but the passenger side had enough clearance. This was due to the shape of the primary pipes not a fault in the design of the Mass-Flo.
This past Sept. I spoke with a fellow who also had the Mass-Flo system and mounted the O2's in the collectors. He indicated that the system ran very poorly until he relocated the sensors at the recommended position. It seems that even though the sensors are heated there isn't enough heat at the collector to get the required signal.
I discussed the fact that mounting in the collector would give a more accurate reading of all the cylinders rather than just one and it appears this is secondary to the heat issue.
As I mentioned above the system works very well with WOT closed loop air/fuel right at 12.5:1 and closed loop at 13.5 which is a little rich but necessary for the cam I'm running.
Sorry but no photos of the primaries with the O2's installed.
DonC