Has anyone ever replaced the upper head drum (HiFi VHS)?
 

Has anyone ever replaced the upper head drum on a HiFi VHS machine? Is it pretty easy making the adjustments after? I have a service manual and scope but no alignment tape. Is a prerecorded or previously recorded tape usable for adjustments?

It's not rocket science but a real alignment tape is preferable.
Assuming you find the same exact upper drum, it can be a piece of cake depending how handy you are

A good example at 3 min mark:
https://www.youtube.com/watch?v=PHuNU8AocEQ

I've replaced dozens in the 80's and 90's. Asti Magnetics sold a rock-solid product back then. Have also installed some OEMs.

Good that you have a scope to look at the FM waveform when adjusting P2 and P3 guides but may not be "absolutely necessary".

The really important thing is to use a "reference standard" tape- one that you know was recorded correctly and is known to play back correctly on (hopefully) at least a couple of VCRs. You don't want to be digging around for tapes AFTER you replace the head.

Good luck on your project!
Brian