you can pick up a T50 box for about $250 depending on model T2 (20 output plines) or 3T (22 output splines) the T3 box is a bit stronger and has a larger input shaft bearing which is inportant to know as dellow sell different conversion kits for both the boxes.
You will need to have the nose of the gearbox machined a bit to accept the the datsun throwout bearing as the toyota and datsun parts are different. you will also need a custom made tail shaft too.
The T50 box is a better choice I believe as it has closer ratios than the Datsun 5 speeds too

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i thought 1 of the benefits of the T50 'box was that it didnt need any cutting of the tunnel?

like blofly said, just a bit of maching of the thrust bearing race and thats it.

all the speedo and everything fits up easier than a 63A or 60A 5spd apparantley.....