WTB. Datsun 210 B310 trans crossmember

Do you have a photo of what you are looking for?

I have a cross member but do not know if it is for an auto or manual gearbox.

The automatic cross member appears to sit slightly lower in the center than the manual. It might still work and you can add spacers under the rubber mount between it and the transmission.

Ive noticed on some Datsuns cars that there are three threaded holes on each side for the cross member. The automatic uses the front and middle holes and the standard cross member uses the middle and the rear most holes.

You can use the auto crossmember as Datzenmike says with some adapter plates. Pretty easy job actually.

You just need 2 steel plates about 2 by 4 and 1/4 inch thick or so. I welded one bolt onto mine years ago to make it easier but it isn't really necessary. These will let you take up the difference in height and let you put bolts back into the threaded holes already on the body. From memory you might need to drill one extra hole in the crossmember to get it to line up with the hole on the body but I'm not positive on that.