The 78LMT is not a great board, even for a budget model, for overclocking. The VRMs don't even actually HAVE heatsinks on them, as you can see on the pictures of the motherboard at the link you posted. I wouldn't overclock on that board at ALL if you need to adjust voltage to any degree. A small multiplier only overclock might be ok, if you use a stock style, not stock but stock style, cooler that blows down towards the board to offer at least some cooling to the VRMs. A tower cooler won't assist with cooling them as it blows horizontally rather than downward, known as top down or downdraft.
The Scythe Big Shuriken 2 might be a good choice for this style of cooler, if it's available in your area. If not, one of the other aftermarket top down coolers made by Noctua, Phanteks, Cooler master or another good name brand (Not one of their 20 US dollar models either). Or, getting a small 80mm fan and rigging it to blow directly on the VRMs seems to have worked for some people on this board in addition to a Hyper 212 EVO to cool the CPU.