I need to install this version to review a course I took many years ago. I can't seem to find a trustworthy source and Keil appears to be wanting some sort of license from me which I'm not sure I ever had. Suggestions ?
If you don't have a valid license, you can only download and use the latest MDK version as an evaluation version or as 'Community' edition. So version 4.74 is now only available to customers who purchased a license. However, you could use the latest MDK and install the so-called legacy pack (https://developer.arm.com/documentation/101407/0538/Creating-Applications/Tips-and-Tricks/Use-MDK-Version-4-Projects). This adds the MDK 4 folder structure to make the latest MDK compatible to MDK 4 projects. Since the Arm compiler version 5 is not part of the MDK any more, you probably have to install it manually (see https://developer.arm.com/documentation/ka005073/latest)