Sorry for the delay. It is 40" from center of joint cap to center of joint cap but I have decided to move the axle back 5.8". So I guess it will need to be 45.8". The axle is a Dana 60 in a '76 F250. Thanks
Oh forgot to add that this is with no body or engine or anything. It is a frame and axles and transfer case only so it will be a little bit shorter, I would imagine, once I add the weight of all of that.