Where does the manga for Beyblade original series end in comparision to the anime?
The Bakuden Shoot Beyblade manga by Aoki Takao is the basis for seasons 1 to 3 of the original anime series. Episode 51 of season 3, G-Revolution, correlates to chapter 3 (the final chapter) of volume 14 of the manga. Chapter 3 of manga volume 14 does not correspond to G-Revolution episode 30.

Spoiler for final pages of manga chapter 3 and episode 51:


   Taichi and Kai stand poised to battle one more time, but the battle itself and its results are not shown. 


G-Revolution episode 52 features


  a giant vortex crisis and then wraps up with showing images of every team and major character that appeared in the entire 3 seasons.


The contents of that episode are not covered in the manga.

Manga volume 14 includes a manga version of the Bakuten Shoot Beyblade The Movie: Gekitou!! Takao vs. Daichi direct-to-DVD anime film.

Volume 14 also features an epilogue one-shot manga about the children of the main characters (who are now grown up). This epilogue was not animated.

Finally, Aoki Takao commissioned novelist Tachimori Megumi to write a Bayblade gaiden (side story) short novel titled Bakuden Shoot Beyblade Gaiden -Yuriy Ivanov- for which he provided the illustration, which is free to read on his official website. Fans have made an English translation of it here. This novel was not animated.

There was also a spin-off manga from the original series titled Seidoushi BLADERS -Beyblade Battle Story- written by Miyazaki Masaru and illustrated by 印照 (whose romaji name I can't find anwhere. It might be pronounced "Shirushi Shou" or "Shirushi Teru"), collected into 3 volumes. Its content is not depicted in the anime at all.

Fans have discussed some differences between the manga and the anime in this forum.

You also mentioned the English-language version of the anime. Since the English dub contains a large amount of edits from the original anime, the dub version does not match the original manga closely. You can see the dub changes from the original anime listed here.