diffirent kinds of pistons

[po12nh d]

I just picked up a sohc that has flat piston and from what I remember last time I took apart my other sohc the piston wasnt flat, it had 4 valve relief. What I wanna know is could this be from a newer sohc.. My old one was a 1990 and I'm not to sure about the one with the flat piston, and would it be ok if I was to re use them?

any help will be appericiated..
one more thing. if you know any good web site to purchase parts to rebuild a ka24e post them on here..