I'd try
Code:
Fedco# Height Width Thickness Inlet Outlet Make Model Years
2-549 6.25 6.375 2.625 0.625 0.5 Nissan 210 80-82
2-549 6.25 6.375 2.625 0.625 0.5 Nissan 510 78-81
2-548 6.25 6.125 2.625 0.625 0.5 Nissan 210 76-79
2-551 5.25 6.625 2.625 0.625 0.625 Nissan 240Z 70-73
2-554 6.375 6.75 2.625 0.625 0.625 Nissan B210 74-78
2-547 6.375 6.75 2.625 0.625 0.625 Nissan 310 79-82
2-554 6.375 6.75 2.625 0.625 0.625 Nissan 200SX 77-79
Check them out at heatercore4u.com (but buy it locally: it'll be cheaper).
They're the smallest cores that are 2 5/8 inch thick.