Why repower

Mostly because Cummins has good marketing.  I haven't been blown away by their engines, but they do seem to have CONSISTENCY or predictable performance.  

I live in an AC pocket of the country but have only heard of a repowered AC and never have seen one. I have seen two or three deere repowered with cummins.

You have to realize that AC has not built a engine in 25 years and to keep up with todays higher hp you have to go with a newer engine. I think the 426 was/is one of the best engines ever built, but to get higher hp you go with a cummins or other brand that is larger and newer. My 4w305 loss some of its character when the cummins was installed and I miss the twin stacks, but it also brought it up to run with the latest and strongest of the newer articulating tractors without loading the crap out of the old Allis engine. Its kinda like saying, if the WD's were so good why did they make a D series.

 The main reason a Cummins engine is used is price. Plus who else is out there building engines? You cant buy a JD Diesel and put it in a CaseIH product . Cat  didnt make a small engine at the time, they did make one for the past few years but even they have sold there engines to Navistar(International) So they are out. Navistar offering was a V8 except for the 466E which is a far better engine than the 359 Cummins but its a large engine size wise for smaller applications and no 4cylinder offering like Cummins had. The next would be a foreign built engine but that doesnt go over well here in America, so Cummins wins by default not because they are the best, most reliable choice. I like Cummins engines dont get me wrong, I own 2 N14 in semis, one 855 in a Steiger and 3 5.9 In some feightliner FL80 the 5.9 in an FL80 is not a great choice by the way the 8.3 would be a better choice, but they make a good engine, but I still think the Allis Chalmers engine is better, more character, more power, more exciting to drive. You wouldnt replace the engine in a ferrari with a chevy, and thats what your doing with an AC engine, with the exception of the 4W-305, I like the 731 engine but I thought it was a mistake, and a costly engine to build for such a small application, in that case an 855 would be the correct swap, or if you wanted to spend the money convert it back to the 844 it was suppose to be.

wht repower so I can buy the 426 blocks and cranks cheap lol

Maybe he should have turned it up to match the others. I can tell you that back then many companies turned out tractors with quite a bit more power than they were supposed to due to poor quality standards. Maybe the 8070 was right on but others were over horsed or maybe the 8070 was low. The Allis dealer where I worked at one time got a 200 from Allis (long before I worked there) that only produced 85 hp. It had the wrong pump installed. New pump and then it had more than 110. Supposed to be about 95. Most were at least 110. In fact they said they had never before dynoed a 190xt or 200 with less than 100 hp from factory. They dynoed all new tractors before sale.