Gear ratio for 7 1/4

if you plan on pumping up your 273 and put 410 in the rear the 7 1/4 will not last long. They are weak and not really meant to be behind anything with performance. I was able to find a set of 3.21 rear gears about 10 years ago available from online rear diff companies. I would only trust a 7 1/4 behind a slant 6. Even though the cubes from a 225 to a 273 is minimal, the torque is higher and that is what will destroy the 7 1/4. I have blown out quite a few 7 1/4s even behind lightly modified 273s

8 3/4 is the best option but pricy 8 1/4 is a good choice too but as with everything getting very hard to find.