I made some tweaks to the original re-mix I uploaded, I incorporated the band clamps into the body, its now much more streamlined.

The screws are 8-32 3/4" should work even though I show 1", if you have a screw cutter then you can customize the length based on your band thickness.

The fender washers are from mcmaster-carr, these are located under the nuts, the idea was to prevent localized force right at the nut to prevent warping pf the clamp, the washer increases to footprint, when you slice them, set the layer stop so you can insert them, then continue printing. If you wanted to use a different size you will obviously need to modify things.

Also with the listed washers you still have to drill out the center hole to fit the 8-32 screw, I couldn't locate the perfect washer, so this was the compromize.

The #8 washers go under the screw head to once again distribute the force a bit and prevent the frame from marring. I used truss head screws as they have a wider head, but standard screws would be fine also.

I printed these in wood filament, I like the feel of these filaments much better for this type of thing, just feels less plasticy and its sands better to smooth out the edges. Once I sanded things I sprayed the frame with a mat poly to add some protection. I used two different colours just to add a bit of spice, which is obviously optional

The clamps were printed in PETG mainly because I wanted the section that the fiber optic to have better light transfer, not really sure it it helps at all but the optic clamp was printed in clear and black PETG.

For sizing I found I got good results with the following, I'm sure alot of this is due to the material and my printer, plus I'm sure the models are not perfectly mating if printed at both the same scale.

sizing

sling shot body: 100.7%
clamps: 100.3%: Seems about the perfect fit