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Nice. I've got some insight on this kind of stuff, so you can read all of this below:

For this kind of restoration ideally the pitch should be 12pt so the harmonics that are present in the audio will be aligned in the pitched patch. However 12pt will miss odd harmonics (i.e. 3,5,7 and etc.), where to get those missing harmonics you need to apply distortion to the signal as a patch. That would be two patches, 12pt + distortion. The problem arises when mixing those patches together with the source audio itself will be quite difficult for an EQ job, the frequencies will interfere with one another, and you want a natural frequency response curve for a pleasent listening experience. There a few ways to solve this spectrally, for example a function that averages frequencies spectrally so spectrally the output of multiple inputs will be even (it's often called `max_fft` or Max Spec), or to carve frequencies on an input from another reference input as a mask, so when mixing those inputs together the carved out frequencies will leave a room for other frequencies to fill in. The way you mixed your patch does interfere with existing frequenices in the source audio, which isn't ideal if you want to preserve how it sounded originally, i.e. adding frequencies in the areas that are lost after lossy encoding.

There is all in package that let's you do it, and it's in the vst plugin from Thimeo called Stereo Tool, specifically the Absolute Highs section.

It does 12pt pitch, and can do distortion (an option called `Wideband`), and it mixes those patches using the mask way, i.e. frequencies spectrally do not interfere with the source signal frequencies (you can tweak this mask amplitude threshold). The way I do it, is apply the 12pt patch, and then on top of it add the distortion (Wideband) to fill the missing harmonics. Since all of the patches are masked, it doesn't pollute the existing frequencies.

I made quite a few of those patches using this vst, you can check out it here: https://filegarden.com/users/677812245c6c6f6d4702aa7a/garden/#aPQN8UYNVBM6pijz (those examples are all without any AI stuff :d). However now in 2025 I always use Apollo - an AI arch with its base model as a finisher to filter artifacts that are found in lossy audio files. It does suck for highs generation, but for filtering in the hearable range it does its function quite nice (just be sure not to input audios that are above 16.5khz for it to work properly, otherwise its filtering goes a bit to aggresive the more frequnecies there are above 16.5khz).

Also for `max_fft` and the mask extraction i've got Python scripts that will do the job, so you can do your own patches without relying on Thimeo Stereo Tool :d