Hi frenchlayer,
DO NOT use stock lifters in your motor! If you use the earlier lifters from the WC-1 motor it will destroy the camshaft in only a few miles [less than 50]. If you replace with the softened version [what you presently have], they will wear at the base [usually in less than 200 miles] again.
When the NE motor was first released [late 2004], I called Whizzer and told them the lifters are too small for the camshaft profile. I made a set of mushroom lifters and sent them to them as a model for future lifters, however they didn't want to go in that direction. Almost all NE motors [late 2004 to early 2007] have the defective lifters, and they finally used my idea of mushroom type lifters in the late 2007 and the 2008 NE motors. Of course it was much cheaper to use the existing stock of lifters and simply soften them with heat. I told them it wouldn't work, and could possibly destroy the motor, and in fact I saw several motors where the exhaust lifter had smashed and a piece broke off and found it way into the camshaft bearing and did major damage to the motor [destroyed the case beyond logical repair on one motor]. On another motor the metal locked the camshaft bearing, the camshaft, and spun the camshaft gear [goodbye camshaft].
If you replace with mushroom lifters, it will enhance the power [just a little] because the valves are held wide open for a longer period of time. But remember the mushroom lifters are to keep your motor running longer, and the side effect of a little extra power is just a bonus.
If you can't find mushroom lifters, it is possible to have a set made by using 1/2" drill rod, or find a set of vintage Whizzer lifters and cut them down [.3930"] to fit the lifter bores in the case [.3937"]. If you manage to locate a set of current Whizzer mushroom lifters, you should have someone drill out the center [way too heavy], reduce the height of the lifter base to between 1/8" and 3/16", and level the bottom [most are ground at an angle and will change clearance as the lifter rotates].
Have fun,
Quenton