Rear seat belts in a 73???

Have just bought a 73 2dr and its not got seat belts fitted in the rear, 2 questions 1. its never had any fitted that i can see so how will it fair at m.o.t time i thought they had to be retro fitted to keep it legal. 2.for safety reasons has anyone got any ideas or suggestions as to fitting seat belts in the rear bearing in mind that the seats are quite often folded up for work. cheers Dunc