My personal definition of crossover is this:
Usually between 68-78 ish & was the sounds that were in the transitional period between the raw 6ts sound recorded on 4 track in a shed, to the more sophisticated disco sound using up to the minuit technology, the term crossover first appeared in the context that we use it towards the end of Stafford, I think, & my opinion is that it was a get out of jail free card for 6ts only DJ's who had burned their bridges by shunning more modern sounds & the modern DJ;s who had shunned the 6ts sounds, they could play sounds from either camp, that didn't quite fit into either camp with out losing face by pidgeon holing the genre as 'crossover'
PHEWWWWWWWWWWW what a load of bollocks, but thats my theory any way, crossover being my fave sound.
Couple of classic crossover tunes:
Darrel Banks- I'm the one who loves you
Ruby Andrews-Just loving you
Current fave:
Stan Martin-Big Mouth Woman
Hopefully food for thought
Russ