About this step I wrote a full article some time ago on my blog. It's in italian language but it is automatically translated. You can found my article here.
After prepared the ambient, upload the code on the Digistump.

Print the parts (STL file are provided here). I've used a resolution of 0.1: there will be a lot of time but enclosure will be very precise. After printed the part, insert the 4 M3 inserts in the corner holex of the box

You must solder cables on the boards pads first than fit in the enclosure. Place boards in their slots, take measure for each cable, cut and sold.
Those are the connections (or see the schematic in the attachments):

• 9V Battery : (+) => Digispark Vin, (-) => GND
• MAX6675 to Digispark: SCK=>D4, CS=>D3, SO=>D1, VCC=>5V, GND=>GND
• 0.91" OLED to Digispark: SCL=>D2, SDA=>D0, VCC=>5V, GND=>GND

Don't make cables too long or lid will not close properly. Don't attach the thermocouple now: will be the last part to be connected.

Boards will be stuck in the slots. If not, you can use some double sided tape or a drop of glue. OLED display can be fixed using a small part of scotch behind

Attach the thermocouple cable on the MAX6675 breakout board respecting negative and positive. Pass the cable into the frontal slot and slide the cover for the slotted hole

Place the lid and screw the screws. Maybe the lid holes are a bit of--centered respect the holes on the box: I'll fix this one day.