big bolt pattern brake drum help!!!!!!!!!!!!!!

[340dart]

Hi my name is chris, im 15 and i have a 69 dart and i currently have the 5x4 bolt pattern.  i want to upgrade to the 4.5x5 bolt pattern.  my question is that if i change the drums/ backing plates will this give me more or less backspace??  or keep it the same.  and has anyone ever heard of a 66-70 b body slant 6 of having the big bolt pattern but using my a body backing  plates  (1 3/4 brakes)   

thanks chris

[Lars]

Never heard of a setup like that. The backing plates are only part of the problem, the axle length really is what determines the backspacing. From what you typed it sounds like you want to put B-body drums on the front of your A-body, am I reading that right?

[Jim_Lusk]

You are really better off matching backing plates and drums. You will need to get new axles, too.

[340dart]

sorry i sould had got to the point.  what i want to kno is if i go to the b body setup will the overall width of the 8 3/4 change or be the same??

[Jim_Lusk]

It will change slightly as the axle offset from the housing flange to the axle flange is wider on all other car lines.