Question about backing plates

The drums I have for the 7.25 rear are 9" SBP. My plan was to drill out the 5th hole and use the backing plates on my 8.75 but I've read on other forums that there would be offset problems. That's why I decided to just use what I have until I can get the parts that I need. My plan is to put a 318 in the car. I should be ok with the 7.25 rear as long as I don't stand on it.

Lots of good info there 72, Thanks!