Emerg brakes & brake locks

[fun in dirt]

We were seriously hijacking another thread so...

The question always comes up about the e-brake when change a 14 bolt over to disc.
Yeah if you can find the Cadillac calipers that'll work (some say not real good though). Anyway, I was planning on installing some type of manually operated line lock to hold the brakes. Yes I know this is not supposed to be used for long periods of time because WHAT IF it leaks down?...Whatever, if I'm out of the truck that long I'll throw a block behind the tires.

So "Big Port Jimmy 6" suggested a Mico brake lock http://www.mico.com/products/displaysubinfo.php?id=37 They do have some cool looking stuff & I particularly like the lever lock style. $275 not a bad price considering it also has a built in low pressure switch & such.
But I'm doing a budget build here & like to know my options and what COULD work with less money.
All to say, I was originally thinking about using a hydraulic ball valve in line to do the same thing. However I noticed on Mico's sight that they have different options if it's for hydraulic or brake fluid...why does this matter? Is there a difference as to how the fluids effects orings, packing, etc?
Also ball valves have all different pressure ratings from 500 to 10,000+ psi...What is the pressure in a brake line?