You do NOT need an 18 spline gear box. That is straight nonsense.
If you are going to run a stick the last thing you need to consider is how much horsepower you have.
I can take a 170 inch slant 6 and blow third gear out of an 18 spline box so fast it would make your head spin.
Clutches, I should say junk clutches break transmissions. And most of the stuff out there is junk.
If you buy a B&B pressure plate and a GOOD organic clutch disc (like the Ram part number 327 which is an 18 spline hub but they make it in a 23 spline I just don’t know that pert number) and make sure that pressure plate is 2200-2400 pounds with no centrifugal assist and you’re golden.
It will drive nice, it won’t break parts if you start beating on it and the lever ratio on the B&B cover is nicer to drive. IMO anyway.
I can say that clutch manufacturers are their own worst enemy in that they won’t or can’t educate the end users on how clutches work and how the APPLICATION of that clutch will break the very best gearboxes out there.
Clutches break parts. That is JUNK clutches break parts.
A very smart man who posts here has a saying that is so perfect that I’m going to paraphrase it here. He is 100% correct and his words are so perfect that I can’t say it better than he does. All credit to him and if he wants to come on here and correct me if I’m saying it wrong he can. But I’m pretty close to his exact words.
In a stick drive train there has to be something consumable. Something has to wear out or something will break.
That point in the drive train SHOULD be the clutch. More specifically the clutch disc so be that wear point.
If the clutch disc is aggressive and the plate pressure has too much spring load (pressure) it will break the weak link in the drive train.
If it’s the U joints then you fix that. Then the driveline will fail.
When you finally have everything full on Brutus sized you will brake 3rd gear.
Then you are screwed. There is nothing we can do to make 3rd gear any stronger. You can cry the gears, REM finish them, switch to 9310 gears, which don’t come in overdrive if you can still get them in any ratio.
And a junk clutch will kill all that trick stuff anyway.
If you want a stick do not buy a clutch based on its HP or torque. If you do, and the lying clutch companies talk you into a clutch rated that way don’t be surprised when it breaks parts.
Shame on those clutch companies for decades of garbage clutches and piss poor customer support.