Definitely That Girl and Reach Out - those are great songs, and Somewhere in Time, in that case, would be hailed or plagued as a true Turbo album of Maiden. If they added Juanita on top of that - straight into Selloutica territory, ha.
To me, I think the only song from the
SiT sessions you could feasibly pull off including it into the album without derailing the established theme and tone is Reach Out. If we're going by the longstanding "no covers" policy on Maiden albums, that disqualifies That Girl. Then again, if you take it a step further, Maiden also has a "no outside writers" policy, which would disqualify Reach Out. For my experiment, I'm willing to overlook that one when it comes to
SiT. BUT, you could also overlook the no covers policy if you like That Girl that much. No rules except what you decide when it comes to what would fit the album or not.
Haven't listened to it as a full 9-track
SiT (only the songs on either side and the song itself), but Reach Out slots in and sounds pretty natural when placed between Stranger in a Strange Land and Deja Vu. It's kind of like a Wasted Years for the album's Side B, even if it might be a tad lighter and more radio-friendly...and it adds some welcome variety by having Adrian take the lead vocals and Bruce on backup.
Others I've put together but haven't tested in full listens are the debut including Burning Ambition and Invasion, and adding Women in Uniform to
Killers (a cover, yes, but an official A-Side single and also included in the Australian version of
Killers. My brief listens so far found BA and Invasion don't sound too out of place. Meanwhile, the shift into WiU's more garage-y guitar sound (especially in the intro riff) is a bit jarring. The fadeout does transition well into Prodigal Son, though, when placed in its Australian tracklisting.
Also working on finding a home for Wicker Man in Bruce's
Accident of Birth since it was written during those sessions, but not finished until the Best Of was being put together. I don't know if I want to do the same with Return of the King and Eternal for
The Chemical Wedding, though. Eternal's too Floyd-y and wouldn't fit, IMO, and RotK is good, but not sure it's good enough to risk putting a dent in the overall quality of the album.
But yeah, I agree adding That Girl, Reach Out, and Juanita at the time, the album could've easily been received as a
Turbo-like or worse.