1) check the input shaft size on the new gearbox, it should match up with yours. Either way, just fit a new clutch to match the gearbox, crazy not to put a new clutch on while box is out!
2) Yes it will bolt up fine, not sure if the ratios will be any good though, the 1600 box is a very close ratio box so wont make the best of the 1600 diesel torque curve id have thought. Only thing to check is the size of the driveshaft flanges, your diesel may have 100mm whereas the 1600 will be 90mm. Also you'll need all the 5 speed linkages and even the stick itself IIRC to make it work (assuming the 1600 box is a 5 speeder)