I said if the Moro arc is adapted to the anime and Moro vs Buu happens, they would scale to that. Not that I am using the manga.
That's hard to define. We know Base Goku spars with Uub on a regular basis, who at least has the innate power of Kid Buu and five years of training with Goku. We know Base Goku (after deaging) can defeat opponents as strong as 'Majin Buu' (Which I think refers to Kid Buu but I'm not certain) which sounds impressive but Pre-ToP Goku could fight a trained Buu toe-to-toe in base form.
We can compare to, say, Baby. Baby was too powerful for Super Saiyan 3 Goku to handle but Super Saiyan 4 Goku could beat him. We can not define whether or not GT Goku chooses to just not use God Ki over SS4 due to SS4 being superior or, perhaps more logically, he doesn't use SSG or SSB due to his child form being unable to use his god forms due to God Ki being too potent (or something similar).
We could either claim SS4 > SSB in this timeline or Goku doesn't use SSB and SSG due to God Ki being too potent for a child body.
Either way, we can scale that Kid GT Goku is stronger than Majin Buu in base, so, maybe stronger than his Pre-ToP Adult Base (who was comparable to Majin Buu). This places Base GT Goku far into 3-A, but far weaker than SSG Goku, Wrath Broly, etc.
SS3 GT Goku could handle Super Baby but lost due to his stamina in his child body being too weak to outlast Super Baby. Super Baby is Vegeta but heavily enhanced. so an Adult SS Vegeta with 5+ years of training + enhanced by Baby is comparable to SS3 Goku. Vegeta was practically equal to Goku in Pre-ToP, this Vegeta should be much stronger and doesn't have the excuse of being weaker due to a child body.
Baby arc SS3 Goku >/= Post-ToP SS Vegeta (Baby enhanced). Still only vastly into 3-A. Still much weaker than SSG Goku and Wrath Broly.
However, Adult Goku in SS4 is capable of effortlessly stomping all over Baby, scaling him far above Post-ToP SS Vegeta. While the gap between SS and SSG is unknown, it can be argued that SS4 Goku would finally be approaching that level of power.
SS4 Goku and Great Ape Baby were complete equals, meaning SS4 Goku is 10x stronger than his SS3 self (who was equal with Super Baby). This places SS4 Goku as far stronger than Post-ToP SS3 Goku, in all likelihood. But still questionably gapped from SSG Goku and Wrath Broly.
SS4 Goku, enhanced by the others, easily defeated Great Ape Baby. Thus making SS4 Goku far greater than the 10 x SS3 figure. THIS is where I would argue SS4 Goku would objectively scale to SSG Goku/Wrath Broly levels.
Later, we see Goku, as a child, can easily defeat Frieza and Cell. Frieza scales above Post-ToP Base Goku, due to fighting Broly for over an hour straight in Golden when RoF Frieza was equal to Goku, in the movie, in base and inferior to Goku in the anime. This means Child Goku is far stronger than Post-ToP Base Frieza, thus placing GT Goku as equal to Post-ToP Base Goku.
GT Kid Goku > Post-ToP Goku (God forms exempt).
The scaling seems to die off here. We know Syn Shenron is far superior to any other Shenron and we know FPSS4 Goku can defeat Syn Shenron in a fair battle.