Some of the smaller system 4 tanks look like they will take 2 35mm size adjusted reels, but they will not quite fit.

The bigger downside is the S4 centre post for this small tank in question is about 1/4" shorter than the 2-35mm reel capable SS-4 tank post.

Yes, I mixed mine up, and got fogged from the light leak betweeen the SS4 funnel and the too short center post.

Live and learn...