66 dart rear end swap

I have a 66 dodge dart and I have what I believe to be a 7 and 1/4 Rear end and have found that it will not hold the power of the swap I am doing from slant 6 225 to a 318. I was wondering what rear end I should use. I was thinking a ford 8.8 might work but I don't know how I would go about shortening it or anything. So what rear end would you recommend. It's My first engine swap and needing some help. Also if you know where to find tranny mounts for a 727 that would be great. But basically what's an easy and cheap way to put a new rear end in my dart. I really want something that will just bolt up. I am guessing the 73 f250 rear end I have won't work lol.