More Prevailing Wage/Davis Bacon Fun

Plan has 1 YOS/age 21 for pretax, match and nonelective.  Based document (not AA) has language that indicates no age/service requirements to receive DB contribution.  So in theory, all employees are eligible for DB contribution. However, to actually receive a contribution you must work a DB job. 

Here are my questions: 

1) For ADP/ACP, do we only include those with 1 YOS/age 21?  What if someone received a DB but did not have 1 YOS?

2)  Plan is top heavy, of those employed on the last day of the plan year, who receives the Top Heavy allocation?  Only those with 1 YOS/age 21?

3) Can the Davis Bacon contribution be used to off set the Top Heavy obligation?  The plan has the option to use the DB as a QNEC for ADP or to Off set ER contribution.  Does this matter?

1 - you're allowed to test the over/under group seperately

2 - anyone who is a participant is entitled to the TH minimum if they are employed on the last day of the year. DB eligibility is usual per some schedule attached to the document granting prevailing wage contributions to some people. If if is drafted right in the document only those under 21/1 who actually get a prevailing wage contribution will enter the plan before 21/1 and will not bring in everyone. If you don't have short service HCEs getting prevailing wage contributions that should be fine.

3 - The Davis Bacon can't do both as I understand it. That is if you use it ADP you can't also use it to offset TH and vice versa. You get one or the other.

But in practice we don't currently administer any davis-bacon plans so someone who works on them regularly might have more insight.