They will NOT drop on, the spring seat locator is too big and they will not go over it, secondly you can not machine the spring seat itself down or you will hit water, this means you can not get enough installed height for the taller LS1 spring. In order to use an LS1 spring you have to have the spring locator machined smaller to fit inside the smaller diameter spring and you have to find a longer (probably custom length)valve to get the proper installed height.
If you are carefull however, you may be able to run a chevy V6 valve spring for the 3.1 3.5 engines. If the .506 lift is with the 1.6 rockers you can probably get away with them but you need to check real carefully for coil bind. If the lift is .506 with a 1.5 and you are useing 1.6 factory rockers it will get into coil bind. I am running them right now on my 360 with a comp XE268 cam that has .320 lobe lift and factory 1.6 rockers. Those springs drop right on and work great to 6000+ a little more, I have not found valve float yet