Bought mono blocks, now spkr cables too long

So long as the cables are shielded, coiling is not a big deal.  Huge problem with unshielded cable.  
You make a good point though that shorter cables are far more appropriate with mono-blocks. 

Get them cut to desired length as others have said and terminated properly. An 8ft pair is probably more common than a 12 ft so can probably sell the longer portion more easily. 

So maybe its a message to those destined for monos. A mono plus is shorter cables.

It is. The advantage of monoblocks is short speaker cables- so you get more impact and greater resolution without adding brightness.

The advantage of monoblocks is short speaker cables- so you get more impact and greater resolution without adding brightness.

     Agreed!

emergingsoul OP
I’m running a pair of XA 60.8s to the Magnepan 30.7

Just back from hols, keep the 12ft cables you have, as those XA60.8’s "could" be replaced in the future, as their lowish power in a big room to take those speakers may become a problem after a while for you, with those big mulit paneled Maggie 30.7’s.
https://www.magnepan.com/www/images/speakers/listening.30.7.jpg
And then you may then get a bigger poweramp, maybe stereo again, and you need the 12ft cables back.

Cheers George