Bullet manufacturers, esp. Sierra, are ultra conservative.
The 51 grain starting charge for the 180 grain bullet should be safe enough to start with, you're using a slightly lighter bullet anyway. The data is based on .308 bullets which I never understood, but so long as you don't have an undersized groove dia. barrel there shouldn't be any pressure issues.
Use your chrono to estimate pressures based on velocity. You've reloaded before, just start low and work up. H4350 and IMR 4350 are nearly identical in burn rate: Burn Rate
H4350 is bit slow for the 174 grain bullet IMO. I use it for 150 grain pills in my 7mm.-08 long range loads. Doesn't mean it won't work, just be careful if approaching max that you may be compressing the load. You'll get heavier recoil with the slower powders as well.
Do you vary the distance to the lands (with a comparator), or do you just load to max OAL?