so I got some new spark plugs and they are .708 inches long and the old ones I pulled out are like .460 are the plugs I have going to interphere with any thing mainly my valves or the piston also how do you guys get to the back 2 plugs on the passenger side of a L98

 

Most all small block cast iron heads use the same length plug thread with the exception of the Vortec, which is longer, and the aluminum head uses a different length if I remember correctly.
Don't know about big block.

 

If the plugs are too long you risk hitting the piston

Take the new plugs back and get the right size