Something isn't quite right. 45 degree dwell on a V8 would be the points not opening at all, a no start/no run condition. You might be on the wrong terminal of the coil. You can adjust the gap of the points to vary the dwell angle.
Make sure that you have a good ground for the ground lead of your meter. You might have to scrape some corrosion off a bolt head or something to get to clean, bare metal.
Make sure you have the meter set for 8 cylinders.
If you look under the distributor cap at the points, you should note there is a small notch in the points assembly. Next to it should be 2 small bumps, you should be able to loosen the screw just a small amount and use the bumps and notch to vary the gap of the contacts. The bumps and notch should be near the screw.
This is a serious oversimplification, but it sort of gives you the idea.
Think of the action of the coil like a toilet being flushed. The tank is filled up, then the handle is pulled down, causing the water to flow into the bowl and clean out whatever is in there. The tank would be the coil, the rotor pointing to the plug wire terminal would be the handle being pulled, and the points would be how long/how much water is being put into the tank. (Electricity would be the water) The "flush" would be the pulse to the plug. Electriticity moves a lot faster than water, so things can happen a lot more often.
The points give a pulse of juice to the coil, and letting it 'fill up' sufficiently will let enough out when it fires the plug. The Dwell angle is the amount of time, expressed as a number of degrees of rotation of the engine that the points are closed, 'filling up' the coil.
If you want a really detailed explanation, you can Google around until your eyes glaze over and your brains run out your ears; have fun.
The "quick and dirty" way of setting the dwell after replacing the points or having gotten them way out of adjustment is to turn the engine manually until the rider for the points is on the tip of one of the lobes of the distributor shaft. (you have to be careful to get it as close to centered as you can) Then loosen the screw and adjust the gap of the points to .014". About the thickness of a business card.
This should let you start the engine when the cap is put back on. You should then be able to measure the dwell with a meter, to "fine tune" it to the specified value. It's a bit of a 'trial and error' process, involving starting, measuring, shutting down, remove the cap, adjust, replace the cap, then repeat. Then you adjust the timing, and re-check the dwell and adjust if necessary.
There's a reason Pertronix and Crane/S&S kits are popular.
Hope this didn't confuse anyone too much
Scott