The Bosch LSU 4.9 AFR sensor install instructions say to place the sensor at the hottest location.

1706°F is the acceptable running temp.
1886°F max peak for short intervals.

I have dry exhaust Stainless Marine Gen 1 with collector mounted O2 bungs.

I've heard on here to mount the O2s 6-10"s past the collector.

Though technically, the gen1 Stainless manifolds have a large open area where the collection happens...and the joint is above that.

I have CMI ETops - the O2 sensors are in the tailpipes about 5 or 6 inches away from the flange and clocked at the 10-o'clock position.

Not sure it helps with your SM exhaust but the concept is the same.

Heat kills , I moved mine further back .. not sure if it helped thou ..I always change too much at once lol

Thanks Dan. Good info on the Holley system install manual.

Probably the hottest location is a few inches past the actual tube merge point.

Adding another concept...should I place the O2 sensors on the same sides of the twin engines...or 1 port man...other engine stb man?

B&M 420 Blower fed.

Ive done it both ways and really didn`t find much difference.

Check, the 420 doesn't load up one side at lower rpm like the Whipple.

I'm thinking maybe the reason for the angled down sensor is to shed condensation?

The 8.3l whipple loads to one side ? Which one?
The condensation question is above my pay grade but I would think it has something to do with the exhaust flow.

Edit: why point o2 down ?
Water.
Lots in vehicles exhaust now too.

Not specifically the 8.3 Whipple per say, just a factor of how they want to spin fast. If they're slowed down, having a factor of poor distribution left/right.

Tried to find the links. Eddie Young may have been the source.

You're running injectors in your tunnel ram if I'm not mistaken, so wouldn't affect your setup.

If I'm off the ball here please tune me up. This is speaking more to the carb'd or pre-rotor injection systems.