The manual FW and the automatic FW are two different animals. You will need a manual FW if you are going to use a Manual transmission. there is no way an automatic FW will work with a clutch assembly.
I did some measuring of the 280 front drive line last friday, and it is short, think it is 13 inches. OH Wait!!! the one I measured is for a 280 with an auto trans. with the 6 cylinder eng and auto trans the trans X mount uses the last 2 holes at the rear of the tunnel.
Your drive line front section from your 240 with the auto trans will be too short to use with the manual trans, because the manual trans is shorter than the auto trans.
You will need this trans X mount.
I have 2 240D drive lines and they both measure about 25" from the front edge of the tri piece to the end at the splines. dont`t know if they are from a auto or manual 240D.
Charlie