Dont think we've used concatenation thus far but have no objections. An observation tho; dont think we have yet been unable to hit the number since the new rules. And @ MikeD - if you dont mind, will add a link to the modified game constraints to the OP.
8*(9*10+42/6)+7 = 783
2,4,6,12,38 - 666 (thought for a minute to go odd but that would have been too devilish...)