Check out this thread:
You would need a related table of contractors that contains the contractor info.
if you have 20 on the job, a portal would be a good way to list them.
Have a Job table
A "Contractors on this job" table linked to "Job" by JobID (one to many relationship)
A "Contractor Info" table linked to "Contractors on this job" table by ContractorID (many to one relationship)
Job Table ----< Contractor/Job Table >----- Contractor Info Table
On the layout based on "Job", have a portal based on "Contractor/Job"
Put fields from "Contractor Info" in the portal along with a ContractorID dropdown to make the link.
Does this sound like what you're after?