I wouldn't buy things like valve springs from an individual on ebay. Summit has some very good prices on cam and kit. I strongly suggest that you buy the cam with the kit as it is engineered to work together by the cam grinder. Get the cam, springs, retainers and keepers all from one source so they will work together. Single valve springs will be ok to leave in the heads to break the motor in, but if you purchase double springs, you'll have to disassemble them and just use the outer springs to break in, then take the springs off, reassemble them and re-install. Now you can see why I said buy the spring compressor. We all need one of those sooner or later.
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