Use the System 6 utility disk image to convert the (North American) System 7 Tune-Up archive into a disk image file that Mini vMac can use.
(This is nearly identical to the British System 7.0.1 install images recipe. One minor difference is that it is a DiskDoubler self extracting archive instead of StuffIt.)
The "Sys6Util.dsk" disk image file, from the "System 6 utility disk recipe".
The "Blanks" collection.
The System 7 Tune-Up archive from Apple:
Launch Mini vMac
Mount the image file "Sys6Util", such as by dragging the icon of the image onto the Mini vMac window.
Unzip the file "005M.zip" (in the "M" folder) from the Blanks collection.
Mount the resulting "005M.dsk" image in Mini vMac.
Open the "Untitled" disk, such as by double clicking on its icon.
Drag the "Untitled" window lower.
Make the "Untitled" window larger.