Ignoring the differences in seat tube angle/length, assuming that both top tube lengths you've listed are the "effective" top tube length, and also assuming it's a 17º stem (which would obviously put it perfectly horizontal with a 73º headtube) there shouldn't being any change in reach going from 74º to 72º. Basically just going ± 1º around horizontal. Cosine is an even function, e.g. 100mm*cos(-pi/180 rad)==100mm*cos(pi/180rad)—so your reach should remain unchanged.* But to achieve this, you might have to adjust the height of the stem by 2*100mm*sin(pi/180)==3.5mm. In other words, just ride the damn bike and don't worry about these little differences.


*bit drunk & sleepy right now so 8th grade geometry skills might need to be double checked.