i want to place a new clutch on my 1975 e20 nissan van?

Question

how do i take the gear box out to replace the clutch

Answer 1

I would suggest you go to an auto parts store and buy a CHILTONS repair manual for your vehicle.
If you don't know how to remove the gear box you certainly will not be able to replace the clutch. putting the gear box back in is a very delicate operation and requires some instruction, like the book will give you. If not done correctly you could damage the clutch or gear box.