Tire space and hoop

To test for rear shock travel clearance, you just remove the spring from one or both shocks, mount the shock absorber only and move the rear swingarm through its entire range of travel, noting any binding, scraping or collision of any moving parts.

Once you raise the rear spring rates and increase the rear height you might find the need to adjust the front fork spring rates to accommodate the change in the rear.

You can't use stronger spring rates to reduce the wheels travel distance, you have to do that with the dimension and mounting position of the shock.

When you are shopping for springs, progressive wound springs will give you a plush ride with less control over spring rate preload, dual or single rate coil spring will provide a more linear spring rate and is generally better suited to racing or a more aggressive riding style.

Fun little bike with a very musical exhaust note, mine was fitted with clip-ons and a TZ yamaha full race fairing. The aftermarket rear shocks I fitted aren't even available now. Best exhaust I found was Jardine 4 into 2 pipes, 4 into 1's had clearance problems.
The stock frame and forks will always exhibit more hinge in the middle feeling or understeer then I like to experience in a motorcycle and modern performance radial tires are near impossible to fit. It's a really really nice but heavy motorcycle engine stuck in a marginal frame. If you turn up the power much and ride it hard you will quickly bag out the primary drive chain which makes it lurch when transitioning from speed to engine braking, if you think swing bushings are a pain to service, wait until you need to replace a primary chain on the CB, that's a real treat.