1700 is the one you want for takedown. The 1750 could probably accommodate them assembled, but would be an oversize bag if flying (the 1700 wouldn't).
My suggestion would be to get the measurements off their website, then cut a piece of cardboard to size (length and width). Lay your guns on it, and make sure you can orient them the way you want, and still have a safe amount of room between the guns, and for your accessories.
I'm actually considering modding a 1700 shortly if my autoloader project works out. Will convert it to hold my kolar and subgauge tubes, and autoloader. Will outfit the inside like an americase with divided sections. I saw a 1700 on here in the past for a trap combo that someone divided like an americase, and really liked the concept. With custom stocks, the Americase 2 gun tube set/auto doesn't work well (too tight).
The Pelican 1700 is also the largest case of its type that will still qualify as a normal sized bag. Depending on who's measurements you use, its either RIGHT at 62 linear inches, or a hair under. The Storm, SKB, Boyt, ect takedown cases are all over 62 linear inches, and the airlines will rape you on oversize baggage fees.