Premiere Pro CS6 - Image size disparity

Question

I have several documentary films. They are all in parts. For example #205 part 2 ; #208 part 1 - and so forth. In my work I need to connect parts in order to create one full documentary. What I did in this example was insert into the timelines part 1 and then part 2. Under video effects / scale - I scaled to 90 so as to fit into the safe margins part 1. However for part 2 I had to scale to 45 in order to fit into safe margins. Once scaled the two segments looked fine.

I then took a look at these two segments/ properties. One was 1920x1080 and the other segment was 720x480. Is there a method to change image size let's say from 1920x1080 to 720x480? - in order to keep consistency? or do I simply keep the two segment both scaled to fit into safe margins, finish the edits, and then -export/ media?

I have no idea how 1/2 of the videos are one image size and the other 1/2 of the videos are another image size.
I am working with AVI format. Let me know what is to be done so that I can finish the project without any unexpected glitches.

Thanks!

What I have and then following the properties of both.

1920x1080 (1.0) & 720x480 (0.9091)

720x480 (0.9091)

File Path: D:\Avi_1984\4015 Chuck\205

Type: AVI Movie

File Size: 24.4 GB

Image Size: 1920 x 1080

Frame Rate: 29.97

Source Audio Format: 48000 Hz - 16 bit - Stereo

Project Audio Format: 48000 Hz - 32 bit floating point - Stereo

Total Duration: 01;02;23;17

Pixel Aspect Ratio: 1.0

AVI File details:

Timecode: User Timecode: 00;00;00;00

Contains 1 video track(s) and 1 audio track(s).

Interleave: 1 : 9.00

Video track 1:

Size is 23.70G bytes (average frame = 227.81K bytes)

There are 112195 keyframes.

Frame rate is 29.970 fps

Frame size is 1920 x 1080

Depth is 24 bits.

Compressor: 'CUVC', Grass Valley HQ

Audio track 1:Size is 685.46M bytes

Rate is 48000 samples/sec

Sample size is 16 bits

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1920x1080 (1.0)