373 swap to 410 or 456

[Cabnchassis]

Originally Posted by BigBlocksRule

Forget swapping gears, swap out the complete rearend. Find a 14-bolt semi-floater with 3.73's. Pop the cover and check gears, swap pinion and axle seals, fill 'er up with your favorite diff juice and you'll be good to go. Complete rearends around here go for $250. They're close to indestructible and even the factory gov-lock works well in the bigger rearend.

I can't think of one good reason in the world to swap a 14ff which his burb most likely would have come with stock for a 14 bolt sf unless you have to have the ground clearance. I have both and while I don't have any problems with the 14sf or the eaton locker, I wouldn't put one in a truck on purpose. It's got way to many extra moving parts. I've seen one throw an exploded bearing race right through the diff cover when it failed, they don't go quietly when they go. Also most of them are limited slip and require limited slip specific gear oil.

My k2500 has 4:10s and I have no complaints. Mine is a 5.7 and you don't notice it's such a dog with those lower gears. Only gets maybe 14 hwy at best though and about 8-9 around town. With a big block i doubt fuel mileage was your worry anyway but you'll lose some doing the swap.

Should you want to swap axles (it will be cheaper but quality is obviously unknown) look at the 3/4 ton burbs from the 90s you should be able to find a 14 bolt ff single rear wheel in 4.10 with no problem, most big block/6.5 burbs I see at the wrecking yard have that dif setup.