The driver for the printer was downloaded from the company's website. It is for the OS9. The installation was fine and successful. The mac is a Power Macintosh 7500/200. It is running OS 9.0.4 (all available updates installed already).
I tried the shift key approach right now (three times). Same as before, the mac freezes when the printer is connected. The printer is a Brother HL-5070N model.
The HL-5070N appears to be a model with three different interfaces (Ethernet, parallel and USB). Which one are you using?
Please note that it is not allowed to connect a parallel printer to the SCSI port of a Macintosh computer. This may damage the devices involved.
Also, the HL-5070N system requirements mention a "Power Macintosh with an Apple original pre-installed USB port". That may or may not be of importance here.
Ethernet is probably the appropriate way of connecting this printer to a Power Macintosh 7500/200.
Chapter 7 in the following manual could perhaps be of interest.
See also the pages 27-28 in the HL-5070N Quick Setup Guide.