The brake warning switch block contains a switch used to light a warning lamp if one of the two hydraulic brake curcuits is leaking somewhere. It also serves the purpose of splitting the fluid sent to the front two brakes.

My switch is pretty grubby. The sliding piston inside doesn't seem to move at all when poked with a toothpick. I think it's corroded in place. It is supposed to be free to slide if pressure on one side is higher than on the other side. This allows it to close the brake warning switch to light a dash warning lamp.

The threaded brake connections are somewhat corroded where the flare didn't cover all of the seat. I'm not sure I want to reintall this part. If I could remove the seat at one end and slide the piston out, inspect and re-ring the pistion, I would be inclined to save it just to keep things original. I'm looking for opinions. I'm not sure if the seat blocking one end comes out without damaging it.

I know there is a service who will rebuild this item for around $75. Do these rebuilds include removing the piston inside, honing any corrosion, replacement of the plastic switch and replacement of the old seats?

What other options are there? Maybe it is okay to split the front lines with a T fitting. Of course the distribution block missing would be unoriginal, but my Hurst roll control won't be "correct" for the car either.

you could T the fronts and run w/o a warning switch.

the brass seats do come out. i dont know for sure but they might be the same seats as come with the master cyl rebuild kits. The only way i've had success removing brass seats is by drilling the hole larger, tapping, and running a bolt in to pull them out. this is service procedure for the master. i've heard some people had success w/ a screw and slide-hammer puller, in order to reuse the seats.

as far as taking it apart, i was a little overanxious with my extra one to see it disassembled, but the center piston only comes out in one direction... i think from the rear, but you have to remove at least the front and rear seats and the connector to do it (i didn't remove both seats, and tried to push it out the wrong way... d'oh).
there are a couple springs in there too, to center it, so you wouldn't be able to move it with a toothpick. The test would be to apply about 100-200psi to one side and see if it goes off center... then test the other side. you'd have to block the outlets of the side in which you apply the pressure. it should also center itself.

as far as using the same block for cosmetic purposes, you could get it rebuilt...
or
you can get a brand new one for about $100 retail. it is the same as for the 67-8 Corvette, but with a different bracket, so of course there is a licensed GM restoration part.
http://www.zip-products.com/CorvetteForum/productr.asp?pf%5Fid=DB%2D509&gift=False&0=dept%2Easp%2Cdept%5Fid%3D2319%26menu%5Fid%3D%26T ree%3D%2C68%2D82%20Brakes&1=dept%2Easp%2Cdept%5Fid%3D2199%26menu%5Fid%3D%26T ree%3D0%2C68%2D82%20Proportioning%20Valves&HSLB=False&mscssid=02F1BF49887DA4F7FAA2C3ADDC3DF5E4
and here is a place w/ guaranteed used ones for $20. some of the trucks of the era used the same block.
http://www.manestruckparts.com/store/store_product_detail.cfm?Product_ID=168&Category_ID=4

most other make model cars of the era also used just a warning switch, but it looked different. as far as i know, only the nova xbodies, camaro, firebird, corvette, and trucks used this one.

Thanks very much Scott. I've looked for this part for hours and only found a "call for used availablity" comment. It's well worth that price so there is no question about the original safety equipment being intact.

You're right. I fogot all about the springs inside. With my luck the switch would start leaking around the plastic onto new paint. The choice is easy.

Did these blockas only come on Z's and BB Cars?

The warning switch block part# 3904270 came on all 67-69 Camaros & Firebirds, regardless of options.

You might be thinking about the rear brake regulator on the frame. It was used sporadically and depended on options. On the bird, it came on cars with a V8 w/ AC and disc brakes.
http://thefirstgensite.com/brake1.htm
http://camaros.org/TopicsofResearch.shtml#Multi-YearResearchTopics
http://www.pozziracing.com/brakes.htm#Converting_Drums_to_Discs