Multiple Employer Plan -- Sharing Excess Assets

[davef]

Employer A and Employer B are unrelated in the controlled group sense. Both have DB plans. Employer A's plan is underfunded and Employer B's plan is overfunded. If the two employers merge their plans and establish a multiple employer plan under IRC Sec. 413©, can the excess assets attributable to Employer B's plan be used to offset the liabilities under Employer A's plan? I'm not an actuary, but it looks like IRC Sec. 413©(4) says that this cannot be done. Am I missing something? Does it matter whether there is a single trust?

Thanks for any help.