Hi John and thanks for helping.

I'm not sure what the refernce points are. The 29.05 inches is what
Lycoming publishes as the length and I'm not sure what their reference
points are. I believe it may be as the engine was presented for its
type certificate. Hence my desire to find a dimensioned drawing so I
could actually see. Right now I plan to remotely mount the oil filter
somewhere on the firewall if possible. If not I would get an adapter
which allows the filter to be attached at an angle. By looking at
photos it seems to me that the furthest point back is the firewall side
of the mags. I'm not sure that is a correct assumption. My engine
mount fabricator indicates that if I have 2.5 inches between the mags
and the firewall I will be able to get them off. I just want to be
sure.

I really don't want to do a swinging mount either. It just complicates
things and the cowl would have to come off to service.

Do you have a dynafocal or conical mount? If dynafocal could you
measure from the rearmost attachment point to the back of the mag or
whatever is the most rearward component of the engine, except the oil
filter?

Thanks. Don...