I did similar last month, here:
https://budgetlightforum.com/t/-/43857
I’ve updated mine from the “wires everywhere, insulated by a oven mitt” version I posted. I’ll take some pics of my updated version tonight.
I made mine wide enough to easily hold 2 two MCPCBs, but not much bigger. That way I can easily do a quick LED swap, but I keep the AL block small to reduce heat loss through surface area. Your block is thicker than mine, which I think is good - the stock I had available on hand was only 0.5inch thick.
I use a laptop power brick supplying one of those CC/CV buck modules, with a PWM module in line for easy adjustability. I like that it has it’s own power supply, so that I don’t have to dedicate any output of my benchtop powersupply (which is under construction) for the reflow block.
I found that one element running at 9.3V is just right for mine. Using the PWM module, 1.6A (~15W) is enough to melt solder, though I usually turn mine up a bit to ~17.5 or 18W and it works a little quicker without overheating anything.
I turned it up to 30W and was able to heat a solid copper P60 pill enought to melt solder a T-Pad quad MCPCB to the pill (though it did take a while to get the pill up to temp).
I also added a set screw underneath to make really tight contact on the heater element, to imporove heat transfer even though the hole was very snug around the elemnt. I noticed after adding the set screw that I got similar temperatures with about 0.5W less power - not sure if it was really necessary, but it only took about 5min to drill and tap an M4 hole.
I sunk my AL block into the wood, so I just can slide the MCPCB off the AL and onto the wood to cool when the reflow is done. Mine just barely chars the wood, very lightly. With the AL block sunk into the wood, I don’t have to try and pick up / lift the MCPCB with still-molten solder LED on it. (I have previously dropped one as I was picking it up after reflow, and the LED went skittering across the floor - this new design prevents that potential issue.)
So far I’ve been quite pleased with it.