Unless MO is all you have on hand I'd use regular old North American Two Row. That's why he has the munich in there. I use tworow and munich as a MO alternative.
which means your two row and munich should be at around 2:1 or 3:1.
medium crystal is going to be around 8-10%
Aromatic and Brown malt < 5%
Chocolate and black patent is a color adjust, <2% each.
that's what I'd start at and then play around.
At 4.9 ABV, it's pretty big for a mild. Which probably explains why you like it so much - American brewers just don't seem to get mild right.
All that said, it's probably a great brown ale.
that may be true with modern milds but historically it was a descriptor of a young beer vs. and aged (stale) beer. There were 8-10% abv milds back in the 19th and early 20th century.