12 bolt to 9" rear end axle question???

[dsster]

1.) For you guys that swap from a 12 bolt to ford 9" did you guys change your axle offset? axle is going to be a Chevy bolt pattern.

gm 12 bolt axle offset is 2.81" while the big ford axle offset is 2.50" im confused since ill be using chevy ends. should i just stay with the 12 bolt axle offset or i have to use 9" axle offset. i don't know if these will affect my break system. Im trying to order a narrow 9" rear end and they want to know whats my axle offset?

2.) Rear end housing flange or backing plates whats the difference? Ive measured the total width of the rear its 54 1/4" from wheel mounting surface to wheel mounting surface how much do i subtract to get housing flange to housing flange measurement?

i know my stock 12 bolt measured total of 60 1/4" from wheel mounting surface and from backing plate to backing plate ive measured total of 53 1/4" which is that gives me 7" difference for both sides. Do you guys think its accurate if i just subtract 7" from the 54 1/4" to get the housing flange to housing flange measurement?

thanks in advance guys

[214Chevy]

I know this is not much of an answer, nor is it much help. But, I don't know much about all of what you stated with all the offsets and all. I just ordered my 9" from Currie that was built to my Chevelle's dimensions and specs. They did all the math work. Unless you are building your own (which I was unable to do), just order one already built form Currie, Strange or any other rear end shop.

[ProdigyCustoms]

We can build a Big Ford bearing end with a Chevy flane and Chevy offset, among other combinations.