oh, if you want it easily removable, use short wood screws to fasten the outside moulding. you only need three screws per side (one on each end and one in the middle).
that will make the glass easy to remove.
The important thing is to give yourself that 1/4 inch wiggle room. Never try to force glass into an opening. That will get you badly cut. Its got to go in easily. The moulding covers the gap anyhow.
That sounds suspiciously doable - the thing is, it’s an old house so obviously nothing is square. I’m not sure that’s enough wiggle room.
I think the door stop moulding is a half inch thick or maybe 3/8 in. So it will cover quite a gap. you probably could have the glass cut a bit shorter than an 1/4. just a smidgen. 
In case the window opening is warped…
about the thickness of a nickel gap on each side will give enough wiggle room.
you probably won’t need to do this. But I’ve done it before with doors that were sticking. One nail at the trouble spot is all it takes. Same thing with a sticking window.
If there is a wrap area in the window opening. Drive a 10d (ten penny) common nail through the window casing board and into the wall stud. That will eliminate a small amount of wrap and your glass insert will fit.