you don't have the original seat (unless you have another seat than the one in your pics) , you have a corbin gentry low king and queen. why is this important? because the pans are different and the foam and cover kits you can buy for a stock pan may not work.
Let's start at the basics: do you have a manual? do you have real tools? Please get a camera that is not a potato and take pictures of your bike in the sunlight.
If you have a 1973 cb750 in green then you have candy bacchus olive. If it is in remotely reasonable shape please don't do something stupid like paint it flat black. It's a unique paint color made by shooting blue candy over a gold base, and when shined up it looks stunning. here is what it should look like if it is all shined up:
unless you got a 1974 model (would have a 1973 build date) in which case the color is liberty green:
Ok, so let's talk about what you really need to do. Give that bike a proper once over and servicing:
Before you can even talk about seats let's talk about:
- tires: how old are they? are they weather checked/cracked? do they need replacement?
- suspension: is it leaking? rust? do you need to rebuild the forks (you def need to replace those old as hell rear shocks)? Are the rubber bushings in the rear shocks any good?
- engine: valve adjustment? what's the oil look like (drain and run a magnet through it)? cam chain tensioner condition?
- carbs: for the love of god throw out those pod filters and get a stock airbox. Also how clean are they?
- drivetrain: primary chain slop? clutch any good? chain and sprockets need replacement?
- electronics? everything work?
- swingarm bushings any good? wheel bearings?
- brakes? do they work? pad condition?
Since you are 19 and talking stupid about seats on a non-running project bike I am going to assume you want to "tear it down to the frame". Stop. You don't need to do that until it is time to paint the frame. Make the bike run, make your mods to a running, riding bike that you can use to evaluate your mods, and then when it is all done you take it apart to paint. saavy? good.
Also I don't ever want to hear the words "cut the frame" come out of your mouth. You have a cb750, there is no need to cut anything unless you want to prove to the world that you are a dipshit. Dick Mann won Daytona on a cb750 with all it's frame brackets in place - are you Dick Mann? no? are you Bob Hansen? The rickman brothers? Massimo Tamburini? no? then you don't need to cut your frame.