ive done it with the 50,30,20 id have to go look but im 99% sure that the motor is the same in the 70 also ive even used the mini and they worked fine.
as to the the part cutting one fin of thats not smart you are setting it out of balance its better to shave or trim the fins down to a smaller diamiter vs removing them.
on my 5.5g shrimp tank i have a ac30 and a mini on it yes it alot of flow but if u know how to diffuse the water it works great, that said if u can diffuse the output i would just use the 70 on the tank, i would use the hardscape or use some of that plastic mesh and see if a piece folded in the shape of a C on the output would slow it enough for your preference*i think it should*, or have a piece follow the water on the outtake and have a little float on the surface say 2inch or so should do the trick.
i dont have an extra manual handy unless i open a sealed one to verify there the same motor unit but they should be so try it. also if the flow is to much u can use a drimmel and cut out the boundary so u can turn it to the right more like ive seem people say, many ways to skin a cat just see what way works for u!