Im not home but when I get home ill show you pic of the heatsink and yes its a double.. it holds 2 x 304 boards. They were open to it they even said they better put a small amount rather than as a gift (but they can do it if you ask)..
Think about it, current will always pass through the route of least resistance.I got this diagram from Meijui (i got the 2 x QB-304's combined on one large heatsink), but I just have two questions about it (in red).
So, is it ok as shown in the diagram? I'm just a bit nervous about first time electronics and don't want to blow up an expensive board. I'll be able to start putting it together possibly later tonight or tomorrow
ps. I asked if it should be series or parallel (which it is in the diagram), they said:
"the driver is HLG-240H-C2100B, 59-119V, 2100mA, cause the board is 102-114V, 480mA-1200mA, so it's to be parallel, it's the best economic solution for this board"
Hopefully that diagram helps others too. My breadboard hasnt arrived yet so I can't start experimenting with electronics yet... but at least now I can put together my light!! will start with the 6500k veg one first, i think id rather make mistakes on that than the 3000k flower board 
I ended up accidentally breaking the hinge off, didnt take much pressure though ... the internals seemed to show to me that it seems a blob of solder is preventing the 'gates' from moving ... even with needlenose plyers they werent moving ... I ordered a soldering iron last week so should be here this week, so maybe hopefully i can 'dab' it to let the wire in.
will await Meijiu email. Their tech support has so far actually been pretty good for the most partSorry to hear that my boards seem to work fine.. id go with this set up (graph from hlg website) the one at the bottom so you put your driver to the + and - on one end and just make a little wire from + to + and - to - between the boards.. thats what look the cleanest and you may be able to avoid using the broken hinge! They do provide long cable so ive cut mine to match the distance between the 2 boards.. Keep us posted!I ended up accidentally breaking the hinge off, didnt take much pressure though ... the internals seemed to show to me that it seems a blob of solder is preventing the 'gates' from moving ... even with needlenose plyers they werent moving ... I ordered a soldering iron last week so should be here this week, so maybe hopefully i can 'dab' it to let the wire in.
I'll email Meijui about this problem - apart from this issue i'm happy so far (delivered quick, well packaged, genuine lm561c's, full 'kit' with everything required, solderless DIY, good tech support). I still have the 3000k flower board waiting for hookup also, so I'll test that next
[update] just tried the other board, the exact same problem in the exact same spot
very similar to the 7 3/4" x 22 " i have..
I push mine in and took them out multiple times without any problem they "self lock in" yes but you can still take them out.. be careful because you dont seem to have been very lucky so far lol but it has been a breeze for me.. ive push in and out multiple times (tried to wire them in series first but light wouldnt turn on) so move to parallelI can't remove the other 'board connector' wires though because once pushed in they're self/auto-locked in!
the other 3 board connectors were a breeze for me too, just this 1 (and on both boards, same position) being a problem. All other positions seemingly ok.
The wire you used is probably too thick. With the quantum boards I use 20 or 22awg wireI can't remove the other 'board connector' wires though because once pushed in they're self/auto-locked in!
