difference between a 78 front axle and a 72?
 

I have a friend of a friend who has a 1978 4x4 who got T-boned and totaled. He just had his front disc brakes totally re-built, tie rods etc. question I have is will this whole front end fit under a 72? what are the differences?

Re: difference between a 78 front axle and a 72?
 

Yep, bolts right in. On my 70 K5 I put a 78 3/4 ton's front axle in and the only thing I had to modify was my front brake lines. I had swapped in the 78's power brake booster and needed adapters to mate it to the 70's front hard line and then I found I was going to need adapters to mate the hard line to the 78's rubber brake lines. I ended up just replacing the hard line so I wouldn't have all those adapter fittings.

Re: difference between a 78 front axle and a 72?
 

found out the gear ratio is different than mine, will the rear end fit as well?

Re: difference between a 78 front axle and a 72?
 

The rear will fit, but you will have to move the spring mounting pads and shock tabs. I built a jig and put an '86 Suburban 8 lug axle in mine. I kept my Dana 44 and just put the Suburban brakes on it. Mostly because the 10 bolt was a dual shock setup and I didn't want to go there.