Bought mono blocks, now spkr cables too long

Cut them. 
 Have nice 8ga speaker wire, barely fits in my counterfeit Nakamichi plugs!

   Cut to fit. My 8ga are about 1.5 feet. Amp to speaker. 

@tom6897 What length of cable matters? When does the speed of light argument run out of steam? 20 feet? 500? 5miles? 

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.