454 Flexplate question

[Hair]

71 GMC with Inline 6 and power-glide tranny - I pulled the I6 and put in a 1989 454 from an RV. I have not started the engine yet, still waiting on a carb and a starter. The flex plate on the 454 would not bolt to the torque converter on the power-glide, so I just used the flex plate that was on the I6. But now I've learned that the 454 is externally balanced and uses a special flex plate.
Here are my questions:
1. Do I need to take the I6 Flex plate off and get the correct flex plate?
2. What will happen if I run the I6 Flex plate?
3. Can I buy a 454 flex plate with a hole pattern that will fit the PG torque converter?
4. Will a 454 flex plate fit in the bell housing of the PG?