A couple of ideas based on my last design for filling a Railcraft tank with lava using netherack and magma crucibles....
First, decide how many crucibles you want to run and place a valve for each one on a tank wall somewhere, ideally in a straight line. In addition, place an extra valve two blocks to the side of one of the ends of that valve line.
To illustrate, if tank wall blocks are 'O' and valves are 'X', it might look something like this on a 5x5 tank wall where you plan to use three magma crucibles:
OOOOO
OXOOO
OXOOO
OXOXO
OOOOO
Place each magma crucible directly adjacent to one of the valves. Place a magmatic engine behind each crucible. Also, place a liquiduct on the extra valve you placed (it should now be directly behind one of the magmatic engines) and run a line of liquiduct up the back of all the engines.
Make sure each magma crucible is set to output lava to the side of the machine that is adjacent to a valve.
You now have an extremely efficient and elegant system where the magma crucibles will output the lava directly into the tank all on their own, and the liquiduct will draw lava as needed from the tank to power the magmatic engines. All you need to is add the item transfer system of y our choice to feed netherack to each crucible and you're set. Easy to set up, easy on the eyes, and easy as hell to maintain.
If you want to see the layout in action you can skip to about the 9:15 mark in this video (you'll see energy conduits on the right of the crucibles...pretend those are magmatic engines
). I've set up an identical system since the TE lava conversion nerf and it still worked fine with one magmatic engine per crucible producing enough lava to keep itself running indefinitely and also produce a surplus of lava to store in the tank.