Need help ID'ing crossmeber/suspension/brakes

[19GMC63]

Great info so far... that thread is a great resource. I'll try to check casting numbers for verification.

So I have square body a-arms, and likely spindles as well. Rotors are 1-1/4" wide, so "HD" version brakes and spindles. The metal brake lines don't match square body though, and they look factory and use the factory mounting tabs on the crossmember, which is what leaned me towards 71/72 originally.

So possibly 71/72 crossmember/brake lines with 73-87 a-arms & spindles?