Referring to specific measurements listed; resize the lumber that you will be using to make the swinging bench. Since you will be building the swinging bench outdoors, use pressure treated wood because it will not warp even if you do not stain and seal it.
On both ends of all the 1x2 sections of lumber that you cut, bore a 3/4-inch hole with a 3/4-inch boring drill bit. You need to bore both 16-inch and 18-inch sections. The holes you bore should be centred and placed 1 inch in from each of the ends of all the 1x2 sections. Consider making a template do that you can bore the holes easily.
On a flat patch of ground, place the 3/4 inches thick 5-foot stainless steel rod. Slide 1x2 sections onto this rod. Keep alternating between 16-inch and 18-inch 1x2s until you have slid all the 1x2s onto the rod. The 18-inch sections now need to be swung up whereas the 16-inch sections have to be swung down.
Place 24-inch 2x4 cross braces at the front and back edges of the seat slats. Bore 1/4-inch pilot holes along the length of the 2x4s and then install wooden screws through the pilot holes and into each of the seat slats.
Place the whole thing against a wall by flipping it over. Adjust the position of the seat by sliding it forwards until the seat is at a comfortable sitting angle. Slide a 60-inch section of 1x2 down the wall against which the whole setup id placed. Mark the location where the 60-inch section of 1x2 against the back support seat. Similarly, make another mark, this time coming from the bottom. Draw a straight line to join the marks after pulling away the seat from the wall.
Screw the seat in place by installing bolts in pilot holes which you need to drill approximately 12 inches apart and at both ends of the 60-inch 1x2s.
Now you need to install the cross braces onto the seat. Accomplish this by drilling pilot holes through the cross braces and screwing the cross braces in place. Position one cross brace on each side of the bench before screwing it in place.
Drill a 5/8-inch at each of the four corners of the seat and install 5/8-inch U-bolt in these holes. Attach one end of a heavy duty chain to a tree and the other end to the swing. Do this at both the front and the back of swing but keep front section a little longer than the back section. The wood swinging bench is ready and you can relax on it.