Are the DLE 55 and DA 50 interchangable with regards to mounting bolt pattern?

yup

Firewall? No. They are a little different.
Prop? Yep.
Muffler? Yep.

Joe,

Close only counts in horse shoes, hand grenades, and swapping in a DLE55!

My answer to the original post is NO!!!! is that clear?

DA-50R
78 mm X 66 mm - 66 mm is inline with the cylinder head.

DLE-55
80 mm X 67 mm

Sorry I gave the wrong information. DA-50R is shown.
John

that explains why, when i use the DA50 templates that come with some of my ARFs, the holes dont line up exactly