It's a bad idea to turn these in for Thorium Brotherhood rep since they're so rare, with the only ways of getting them being Molten Destroyers and mining Dark Iron Deposits, both with epically low drop rates.

I just finished https://vanillawowdb.com/?item=17182 [Sulfuras, Hand of Ragnaros], but I had to work HARD farming Molten Destroyers and literally soft reset MC 20+ times to get enough Bloods to finish it that week. That was on top of trying hours of Dark Iron farming in BRD without a single Blood, and already having 1 hidden on a bank alt. There were never any in the AH or sellers through trade either, probably due to the fact that most people skip as much trash as they can, including Molten Destroyers.

The https://vanillawowdb.com/?item=17203 [Sulfuron Ingot]s took way less effort to acquire. Even though they aren't farmable, the drop rate is pretty high off Golemagg(~30%), so there's a good chance you'll see them on the AH, being traded or dropping for you while doing rep runs. You can easily sell Bloods of the Mountain for as much, or more, than Sulfuron Ingots.

tl;dr: Sell/Save any Bloods of the Mountain you find and use only Lava/Fiery Cores for turn-ins, since they have good drop rates on pretty much all the elementals and giants in the instance, especially bosses.

As of today, patch 4.0.3 i guess
I received 2000 reputation upon handing in this quest.

Please do not do this quest. You're better off by selling your Bloods. Depending on the server economy and the other persons desperateness, the prices for each Blood can vary from 500g to 1500g.

You can get the same reputation by turning in https://vanillawowdb.com/?item=17010"">(Item #17010) or https://vanillawowdb.com/?item=17011"">(Item #17011), which cost around 5g per piece.