Bicycle Tutor

I am highly ignorant of bike matters and am slowly rebuilding a 1984 Peugeot Monaco road bike (and slowly learning through it - the hard way).
Unfortunately, when I bought the bike it only came with one brake caliper (side pull of course) and it is pretty decrepit and the wheels aren't original.
So, I foolishly ordered two shiimano Tiagra calipers from ebay that seemed to be a deal, not realizing that wheel sizes had changed and brakes with them. Now I believe the problem is that I have old fashioned 27x1/4 wheels and the brakes made for new 700c don't quite reach the rims. This is in addition to another slight problem of the nut not fitting through the hole in the frame or the screw part of the brake not being long enough to get to the other side (depending on perspective), which is how the old brake caliper fit through (that screw is a full 1 1/4" long with room for the reflector and an indented washer)
My question is: How can I resolve this problem?
If there is some kind of metal attachment that would fit in the old brake hole and provide a new brake hole a few millimeters lower, that would solve the problem.
On the other hand, if there is something along those lines to extend the brake pads lower than the limits allowed by the Tiagra callipers AND something I can use to hold them in the holes despite the fact that the nut wont fit in and screw doesn't fully reach to the other side, that would also solve the problem.
I just need to know how to access either of those things since I don't know what they would be called or where I could buy them.
On the other hand, if such things don't exist and I need to buy calipers that will fit the frame, perhaps someone can tell me how I can be sure I am getting ones that will fit? (and maybe you'd also like to buy these tiagra ones from me... they are brand new!)
And, finally, would 700c wheels fix the problem, or would they just not fit with the frame?
thanks a lot,
-Jason

Probably the best option is to get the correct size brake calipers. You could fit a drop plate or drop bolt but personally I would not:-
http://sheldonbrown.com/dpdropbolt.html
(these are no longer made by Harris cycles)
or
http://sheldonbrown.com/home-drop.html
Deeper drop brakes are available and you measure from the mounting hole to the rim to get the size. http://www.sheldonbrown.com/harris/brake-calipers.html
If you want to fit 700c wheels, at a later date, then these are about 5mm smaller (lower) than 27" wheels, so ALLOW for this when ordering new calipers.?
In your first photo you would have to open (drill) out the hole on the back side of the "bridge" to accept the fixing nut. The same goes for the front one and you may have to open up the hole on the back of the fork. The hole has just to be big enough to accept the smaller diameter of the nut. --- NOT the larger "ridge", as this is the securing part!
The good thing about your set up is you could fit mudguards (fenders?) if you wanted to and also a larger tire. The Tiagra calipers you have are designed for narrow (700x23 or 25) tires without guards. Save the Tiagras for your next project or re-Ebay them?
Probably not what you want to hear but remember we are talking safety here.

Depending on where you live, you may be able to find a good pair of used side pull or center pull brakes. I know there are a couple of stores where I live that specialize in used parts. Make sure the new calipers have the slot that allow you to adjust up and down. I have an '85 Peugeot that I built and used 700c wheels and the original style center pulls work fine on mine.

some folks get away with a round file to make the brake pad slot a few mm longer in order to reach the 700c rims.