Sidemount diving requires a unique configuration of regulators different from twin sets or single cylinder diving. Dual 1st stages with short HP hoses mount to sidemounted stage cylinders with hose lengths for your needs.
Swivel 1st stages make hose routing easy and natural with a 5th port for further flexibility. Mount the 1st stage on the valve and both your high pressure and low pressure can route straight down your cylinder neatly.
Reversible 2nd stages can be adapted so the hose can be attached to either side. Your short hose can be fitted with an elbow to make the hose routing more natural for the backup 2nd stage and a long hose for your primary donate.