P 11 muffler questions

I am considering using P 11 mufflers on an Atlas project. First I need to know the inlet diameter and I assume it is the same as an Atlas. True?
Next, where is the bracket located measuring from the inlet to the bracket.
#3...Is there a baffle plate inside the muffler similar to the Atlas muff? I usually drill it out as big as I can go.

You talking about P11A or Ranger mufflers? The '67 P11 had up pipes with stubby little mufflers. They had a tab inside that could be bent down making them basically straight through. Well at least the aftermarket ones did. No clue what was inside the '67 P11 OEM mufflers. I personally don't know anything about the down pipes on later P11 models. If you are actually talking about 1967 P11 exhaust, you probably need to brush up on your brazing skill and braze brackets where they go. Don't know about that either. My '67 P11 exhaust is a one off 2 into 1. RonL or one of the other P11 restorers should know where the brackets go for all the P11 models.

Maybe what you are thinking about is the N15 mufflers. They could be easier to hook up to an Atlas frame. I was thinking about doing the N15 mufflers at one point, and tried email with Walridge, but Mike at Walridge had no interest in working with me if I didn't know all the parts numbers down to the nuts and bolts. You might have better luck with him.

perhaps N15. reverse cone mufflers down swept pipes

My Matchless G15 appears to use exactly the same mufflers as my 64 Atlas…. They are at the very least the same outside shape. Perhaps the bracket locations differ?

the mufflers in your picture are the same as an Atlas. The mounting holes are probably in the same position. The mufflers I'm talking about fit the down pipes on a P11 and then tip sharply upwards. I can find very few pictures. I know someone who bought a new pair about a year ago but I've lost contact with him.