None of Marcion's original Bible has survived. Fortunately the Early Church Fathers criticized Marcion's New Testamant so much, that just about every verse has been compared with the modern Bible. That is how we know very nearly what was in it.
Marcion (the heretic) was such an awful threat to the Early Roman Church. Considering that most scholars believe that Marcion probably had no idea about any of this, and that his text was most likely the original, what were they afraid of? Were they afraid that they would be caught out altering the Scriptures?