Ah, right. It's because the 4000T doesn't have workbench.library in ROM.
For your original problem, boot without startup sequence and delete/rename envarc:sys/screenmode.prefs
If you've truly trashed the original partitions, you'll need to extract workbench.library from a regular 4000D 3.1 ROM and put it on your Workbench 3.1 and Install 3.1 disks in order to recover.
EDIT:Thomas beat me to it!
