wheel mounting difference Drum to Disk

[kehstr]

did a search for this with no luck.

I have a 72 GMC that we put on a 69 chassis under it since that is all we could find at the time and have wished it was 5 lug to be true to the truck pretty much since the day I finished it. Got my hands on a 5 lug rear axle, so really thinking of swapping it all. My question. How will this affect the front of my truck? Is the measurement from Wheel Mounting surface to wheel mounting surface the same or different between the drum brake and disc brake trucks up front? Also, correct me if I am wrong, but I believe the distance from wheel mounting surface to wheel mounting surface is about 1 inch narrower on the disc brake trucks compared to the drum brake trucks. Is that correct?

Thanks for any and all help in advance