GulfStream was a Florida builder. Actually there have been quite a few companies named Gulfstream, but based on the photo I think this is Gulfstream of Miami. Check for a aHull Identification number on the transom of the boat. On the outside in the upper right corner.
GULFSTREAM OF MIAMI
MIC: MEP Status: Inactive
Company: GULFSTREAM OF MIAMI Company Official: MARCKER, JOE
Parent Company: GULFSTREAM OF MIAMI INC Parent MIC: NUL
Previous Company 1: MEMEGE CORP.
Previous Company 2: GULFSTREAM OF MIAMI
Previous Company 3: MARBO ENTERPRISES INC (OOB)
Previous Company 4: NULL
Address: 2314 NW 150TH ST City: MIAMI
State: FL Zip: 33054
Country: NULL Phone: 3056882691
Fax: NULL In Business: 10/7/1991
Out of Business: 6/6/1997 Date Modified: 6/6/1994
Type: Outboards, Open Motorboats, Jon Boats
Inboards, Cabin Cruisers
Addtional Address: NULL
Also you can check that registration number with Florida DMV.