That losi heatsink does fit. I saw a buggy driver using it on his CC/neu at a race yesterday. I didn't specifically ask if he had any trouble putting the heatsink on, but it didn't sound like there was any issue. He said the motor seems to run a fair bit cooler with it. He ended up winning buggy A.
I use a 50mm x 15mm 12v fan (puts out a lot of air on 6s
) on my 1515 and it makes a big difference, especially on warmer days, but haven't used it in summer to test it properly yet. Now, the heatsink, with a fan should run very cool
.