One degree in seat tube angle is probably not going to make a difference, since seat posts allow some fore-aft adjustment. Assuming you set your bike up with about 10 cm of seat post exposed, the 73 deg seat tube will place your seat about 1 cm behind where a 74 deg seat tube would put it. So all you have to do is adjust your saddle 1 cm farther forward, and the difference disappears.
It all depends on the details - what setback does he need, what is the adjustment range of the saddle/seatpost combination, et cetera.
That 1 cm of extra adjustment might or might not be possible, without a change of seatpost or saddle.