No, you generally do *not* need the special crankshaft installer tool SA9104E (or any similar crankshaft holding tool) when removing the timing cover on a 1999 Saturn SL1 SOHC to replace the head gasket. This tool is typically used to prevent the crankshaft from rotating while you're tightening or loosening the crankshaft pulley bolt. Since you're removing the timing cover, you're not working directly on the crankshaft pulley.
You'll likely need other specialized tools for the head gasket replacement (e.g., torque wrench, possibly a camshaft alignment tool), but the crankshaft installer isn't one of them for this specific stage. The crankshaft will remain stationary, or at least stable enough, while you remove the timing cover.
