Block coolers are very specific with what card you can use them on and usually come down to the model as well. For example, an XFX Double D 760 would require a different block than a different XFX 760. There are some block coolers that cover multiple cards but they usually don't cover all the components. This is to be expected because you are talking about making a block that can somehow accommodate cards with different VRM and memory positions in addition to different lengths.
If you do get a waterblock for your 760ti chances are it won't work with another model graphics cards without signification modification, at which point buying another block would be more prudent.