Here is the situation, funds have been accepted from a non-customer for wire transfer to Cuba. No wire sent, instead funds blocked in an interest bearing account and OFAC notified. My questions follow.

-- What do we use for tax id on the interest-bearing account?
-- Though the dollar amount is only in the 3 figure range, a SAR is warranted as persons subject to US jurisdiction should not do business with Cuba, agree?

I'm bumping as I really would appreciate some input. Thanks in advance.

My understanding is that:
the account would carry the tax ID of the person who attempted to wire money to Cuba....
yes, you'd file a SAR.
(Note, whether to file a SAR is something of a gray area, but the guidance I've been given consistently is to report to OFAC *and* file the SAR.

Just my $US.02

It may be an allowed transfer. Refer to the sanctions on Cuba, specifically page 4 regarding sending money to Cuba:

Cuba Sanctions

If the transfer qualifies, have them complete this affidavit:

Cuba Remittance Affidavit