Heh. Anyways--You really, really need to drop the PCM audio in favor of AC3, as PCM takes roughly 10 MB of space per minute, and there is absolutely no reason to be using PCM audio for a project like this. I don't know what the runtime of this is, but let's look at the runtimes of the three original films:
Godfather I: 175 minutes
Godfather II: 200 minutes
Godfather III: 170 minutes
Now, assuming this edit runs for roughly the amount of time the three films do, combined, that's 545 minutes. At 10 MB a minute, that's 5450 MB. 545 minutes of AC3 audio at 224 kilobits per second would take up about 915 MB of space, so dropping the PCM in favor of AC3 at 224 would yield a loss of 4535 MB--slightly more than one single layer DVD.
Edit: And having just noted that, according to DFNYC, that this is a mono track, you could cut that 224 figure down to 128 Mono, and that would drop another 450 MB off of the size.
You could drop one DVD from this collection, simply by converting the audio, without even touching the picture. So that takes you down from 5 DVDs to 4 right there. And you could probably afford to do a recompression of the MPEG video--it would take you a year and a day to work with 550 minutes of video, but with noise reduction and some other filters, you could cut this down to 3 DVDs without affecting the video much.
Edit: DFNYC feels that two dual-layer discs wouldn't cut it, let alone 3 single layers, as I allege, but seeing that as it stands now, you're at 5 SL discs, we're obviously not dealing with a bitrate nearly as high as that of the official DVD releases.