Hi Len . . .
The Santucci book documents that head as a 292 casting number. Those pipe plugs are closing off smog ports. A belt driven air pump was fitted to add fresh are to exhaust stream to help the catalyst do its job.
regards,
stock49
PS. Now that I look again at the Santucci book it shows this head having been used on both 250 and 292 truck applications. Our old "late Chevy index" page suggests the same
Late Chevrolet Inline 6 Cylinder head Index 
