Do i have the right distribution block

I need help figuring out if I have the right distribution block for my system. I have 2 amps, a 2 channel for my sub that will be putting out about 300 watts rms, and a 4 channel amp that will be putting out a total of 300 watts rms for four 6 1/2" speakers. I will be running 4 gauge wire from my battery, around 12 feet max. I have a 4 gauge to 8 gauge distribution block, and the 8 gauge wires will be run up to 3 feet long since my amps are spaced so far apart since i have a truck with hardly any room to mount the amps. Would this setup work alright? Will the wire size be alright and the length of 8 gauge wire from the distribution block be cool?

that would be fine but it would be better to run 1/0 gauge from the battery then split to (2) 4 gauge wires