SCCR is the most common and new gear sets are sold. This is straight cut , close ratio gear set that fits the rib cage box without modification, then next come other variations, Wheeler, Richmond, and Taylor, they are all ribcage gearboxes modified used Webster/Hewland type gears like you would find in Formula Ford, almost endless ratio choices, big advantage to this route, is dog gear engagement, and first gear ratio used so you have on track usable first gear, for example we use like 1.6 ratio first gears, so in the slower corners we could shift down to first gear, and this is huge deal, as you can keep the rpms up on the engine in slow corners, making for quick corner exit. This set up is expensive, $3-5K used is not uncommon, if Taylor could even build a new one for you these days, it would be well over $6K. I have a good friend who making dog gear sets for the rib cage, that require no mods to fit to the stock box, that offer the gear ratios we have learned over time that work the best, but he still a way's away from finishing the project though.