Fairly clever, Don.
Initially reading this thread title, I thought it was gonna be about using two elements of dissimilar songs to create a new one.
Something like, say, singing the lyrics of Jethro Tull's "Aqualung" over the music of Neil Diamond/the Monkee's "I'm A Believer":
"Sitting on a park bench eyeing little girls
Eying little girls with bad intent
Snot is running down his nose (do do do)
Greasy fingers shabby clothes (do do do)
Watching as the frilly panties run
Aqualung my friend
Don't start away uneasy
You poor old sod
You see it's only me...."
you can hear it.
Okay, so it wasn't.
But Spastic immediately diverted this thread from Mr Tein's original intent into 'sewn together' XTC song titles.
Which is all well and fine, nothing wrong with that.
However, going back to the original concept of musically
editing together two XTC songs,
I'd say:"Towers Of London" & "Earn Enough For Us"
You'd have to pick a tempo between them, faster than the former and slower than the latter.
And Tower's modulation from F to G already gets you into Earn's key.
An obvious one:"Senses Working Overtime" & "Great Fire"
Tempos and initial chords and keys (Am) are already similar,
and the modular construction of both would facilitate juxtaposing sections
(after resolving modulation and voice leading issues).