The only "attachment" I use for brake bleeding is a 2" to 3" length of vacuum hose to go over the bleeder screw and the end of the Mityvac tube. I put my wrench over the bleeder screw, then the vacuum hose with an appropriately sized hose clamp to hold it firmly on the bleeder. Couple of pumps on the Mityvac then crack open the bleeder screw. Once the clean fluid starts coming out with no bubbles, lock down the bleeder screw and release the pressure on the Mityvac.
I've done this on both the factory Disc/Disc and Disc/Drum setups.
The Motive Power master cylinder cap doesn't fit the Impala/Caprice very well at all. There is interference with the firewall. You have to loosen the master cylinder from the bootster to get it to fit.
I have not had good luck with the one man bleeders. I get a better pedal with the pressure bleed.
95 Wagon suggested a system some time ago that I purchased and adapted to my Motive Power tank.
Maybe search 95 Wagon in the brake section and see what come up. I am at work so I don't have time right now.
A good rule of thumb when using speed or conventional bleeders is to use a couple foot length of clear 3/8" hose and running it between bleeder and a bottle w/ some brake fluid at the bottom. Submerse other end in bottle. You can't possibly draw in any air that way and have never had any issues. Use speed/one way valve bleeders here too.
I suspect those having issues with the "one-man" bleeders are loosening them too much,just barely crack them loose seems to work best.+1 on the vinyl tubing into a jar (is there any other way) I'm tempted to use a wireless web cam to watch the action from inside the car. Fluid changing color,and bubbles stop coming out,etc,etc...