Is this seal for the LE5 TB a stock one? ->

Could please someone tell me, whether the seal behind the plate is a GM-part or not?

I know, we have this green seal for it on the 2.4 manifold. But I would something like this one... not the adapterplate only the seal.

Thanks for help in advance

not as far as I know, I believe it's made especially for that adaptor plate kit

Confirmed. It is from crate engine depot only like Tom has answered to me.