Thanks, iOS v4-v5 Full Rom Files?

[ken olson]

Hi Johannes,
Thanks for your comments!
Since posting have been searching for postings of Open OSes on 32 bit Apple Mobile Devices.
While have found things like "Dual-Boot Android on Your iPhone"  https://ios.gadgethacks.com/how-to/exclusive-dual-boot-android-your-iphone-ios-7-0161123/  closer exam reveals "Thanks for having some fun with us this April Fool's Day! We hope you all enjoyed this as much as we had coming up with it. If and when something like this becomes a reality, we'll have your step-by-step guide ready at AppleHacks.com."
"What you could do is maybe try find a rom image from the iOS v4-v5 times when they distributed the OS as a full rom file. Running an older version of iOS would surely make your device run smoothly (although not as fun as putting FreeBSD on it :)"
Fortunately my 4S still has iOS v6.1.2 so am OK
Question:  While I am a beginner concerning iOS have more experience with Windows OS and have used Windows image files to make bootable Windows USB Drives.
Any suggestions where to look for iOS v4-v5 full rom files?
Did a quick search using "iOS v4-v5 full rom files" but got nothing.  No "..." got "about 8,840,000 results (0.58 seconds)" but nothing relevant.
Thanks again for your help!
Ken