Best way to insulate supply duct with minimal clearance

I wanted to wrap the supply side ductwork, but the return is mounted so close to it, in some spots barely 3/4 of an inch of space between them. What is the best way to insulate in this case? Supplies both heat and AC located in an unfinished uninsulated basement of a 2 story house in Chicago area, basement is pretty chilly right now in March and the supply spans the whole length of the house so there is a pretty large temperature difference when you get to the end of the run 30-40 feet away from the actual blower.

I thought of 2 possible ways I would do it:

1. Getting 3/4" foam board and shoving it up in the space and then use R-6 fiberglass duct wrap on the other 3 sides.
2. Fill the gap with spray foam, as this would also close up any leaks. Then again use fiberglass duct wrap on the other 3 sides.

Supply is the smaller duct on the right in this picture, the gap looks much larger than it is in the pic, on average about 3/4 spacing.