hanlon used to sell a kit to machine the shaft down. The problem is that the cobra mainshaft has a groove for an extra clip that I believe holds down the 3/4 slider that the normal shaft doesn't have. I know for sure though that there is an extra clip there, so what hanlon did is sell a cup that goes under the bearing which presses down on the 3/4 assembly and keeps it from moving. I know on the reg shafts, that slider is pressed on, but I believe (again it's been a while) that the 3/4 slider on the cobra/z shaft just goes on and is held on by the extra c clip, then the tapered bearing gets pressed on after that. I've got one of those trannies under my bench. I'm not sure that he sells this cup piece any longer though, and simple machining won't work unless you find a way to make up for the lack of groove for that extra clip.
I know the shop i get parts from actually has a used z/cobra shaft that they'd sell me for $75...pretty good price. Perhaps I should pick that up.
In the end though, that little cobra pocket bearing isn't a make it or break it deal. It adds I think 10-15 pounds extra torque and allows for more preload on the input for assembly, but that's about it.
I've built 4 z spec super alloy trannies from normal wc trannies so far using the standard needle type insert bearings in the input, and so far so good.
Additionally, there is some interesting info regarding the z spec kits. (I got bob hanlon on the phone the other day and chatted with him for about 20 minutes on this)....with just about every "kit" offered on the net, they're all the same (including the shop that sells me these things locally)...the z kit that's offered gives you a tremec 1,2 gear, but a made in india 3rd gear, 4th/input and india cluster. THis is just a big problem according to bob. He says if you're building a z that you really want to last, you can't run that india crap that everyone is pushing. He said that the problem is that everyone wants something for nothing, and as a result everyone sells the cheap stuff.
I have used the india kit 4 times now without issues, but I do know MFE on the corral busted a made in india z spec third gear. He's replaced it and so far, so good.
If you call up hanlonmotorsports, they can sell you the z super alloy kit for about $350. The gear box sells this same kit for about the same price.
Hanlon told me he can sell the "real" kit with 100% tremec parts, but didn't have a price off the top of his head. Next time I put one of these together, I'll have to get a quote on the real stuff.
JKA, no offense intended..that's why I didn't include any names. Nothing was directed towards anyone specific.
As for myself, it's just a side thing I do with t5's, but I've got about 20 under my belt, and imo that darn near qualifies me as a t5 pro.