I have everything to build my own rigging, just have another couple projects on the list before the sling project begins.
Many people use bow eyes/stern rings on the transom. They are a requirement at some of our hoists.
I prefer the idea of going all the way under the boat at the bow and passing the sling thru the handles to keep the bow strap in place.
Here is another way to do it adding in rings on the front sides.
You will need a lifting point to set the sling up correctly for balance. This can be a solid object or a forklift. Make sure the eye you use is large enough for the hoist you plan to launch from. Some are massive!
BTW the two D rings in the front I use for a towing/anchoring bridle. I built a bridle that is then passed thru the bow eye and has a knot at the end of it. I use a screw lock carabiner to attach the anchor rope to the bridle. This disperses the load over two attachment points when anchored and if one breaks I have redundancy. I need my boat to be there when I get back to the surface.