It's a non-critical dimension and Lovejoy even states a .030" variation is allowable (+/- .015") which is 25% of 1/8". The problem with having the couplers too close on a high pressure pump is that you can have collisions when both shafts grow from heat (engine is producing heat, and pump is producing heat so both will grow under use), and that can lead to bearing failures if you're not lucky enough to merely have the coupler break (like in this thread).
Having them too far apart - you might need a new spider sooner than normal, but +1/16" isn't going to change anything as it's under 10% of the spider's width. So think about that when you decide to argue for them being extra close together - there's no up-side to it.