Sorry, been travelling and I limit my internet usage while driving.
Okay, let's start with some basic info:
What Bad Dog Parts labels as 240 front rails (a poor choice on my part) start 9-inches in front of the firewall, cover about a bit more than a 1/3 of the TC rod box are and end where the stock rails ended. They are made from 13 gauge steel and are 2to 3 times thicker than stock rails. They can be used over existing stock rails or as stand-alone replacements and are sold as singles or as a set.
The optional rear 240 rails were designed for folks who wanted a stiffer unibody, had increased the HP or autocrossed/raced their Zs. These are butt welded to the aforementioned front rails and welded on the member cross member running in front of the rear wheel well. I showed them to Mr. Matsuo and his reaction was to slap his head, tell me they could have made these for $2.00 and gave me a pat on the back and a smile. They are sold in sets only.
To complete the circle so to speak we recommend a front triangular strut tower bar and a roll bar to hold the rear strut towers in place.
The 280 frame rails (the word front is not needed here) also are made from the same gauge steel and start around the same 9-inches in front of the firewall and end where the stock rails do. They are made as a complete replacement or as a cap over an existing rail. Sold in pairs and as a single piece. I would hazard a guesstimate and say that about a dozen people have bought and made modifications to allow the use of our 240 optional rears with the 280 rails (most I believe had installed LS/LT/RB motors).
Both the 240 and 280 rails are compatible with replacement floors sold by Zeddfindings. My street and 240 race car have Charlie's floors installed.
Bad Dog recommends that if your car will be kept stock and you need floor pans then get the best that's out there - Charlie's floors and his rails. If you need something stronger for whatever application then contact us and if you need something even stronger then you should search HybridZ.org for the means via box tubing welded half in and half under the floor pans that will allow you to build a bullet-proof subframe for really, really high HP Zs.