Nice build so far. Welcome to the insanity.
Nothing wrong with a 10 bolt for now. 37’s will push the envelope but if it doesn’t have a locker or posi in it the diff will probably be ok. Look into chrome-moly axle shafts if you break one.
The rear axle snafu you had with the spring pad mounts might have been what it came from. 14bolt axles from 1 tons do have wider spring pad mounting.
One word of caution I can gather from your pics. Check your rear driveshaft angle. Between having a slip yoke on the t-case output and the overall size of the 14b being larger and 6” of lift you probably are going to end up with vibration at speed.
Many, including me have run into problems on K5’s at 4” lift and slip yoke t-case outputs on 208 or 241 t-cases. I worked hard to get the u-joint angles right and while I didn’t have a vibration at speed I noticed a pretty good growl on deceleration I just dismissed as tire noise. The 4th or 5th time I drove that combo as I slowed for a stoplight the growl got worse and I heard a loud clank from under the truck. I limped to the side of the road and crawled under to find the u-joint at the axle had partially twisted out of the yoke.
Typically the fix is installing a slip yoke eliminator to the t-case and installing a drive shaft with a slip section and a c-v (double carden) joint on the front side of the rear shaft. I kept the slip yoke and instead had a custom shaft built with a cv joint. Doing that requires adjusting the pinion angle up to just below the angle of the shaft.
Good start so far on the project though. Kept it up!