Lost wax casting and cores?

Hi!
I'm sitting in front of my computer and drawing along for my next
project. It's a scale model of a Diesel engine built 1906.
Looking at the various parts, I have to lift my hat for the enineers
that built it. Even more ingenuity in the shop that built the patterns!
The base plate is so complicated that I do have to use lost wax casting
(and silicone forms).
Right now, I'm thinking how I could cast the valve head that I have
drawn (paper is patient). I _need_ to have core prints in the casting.
Is that possible? *)
And if yes, how do I make the cores? Do I use the same "plaster" and
cure it in a silicone form? Can I stiffen the core print with some (SS)
wire?
*)
I have to admit, that I do have _very_ little casting experience and I
know that I will have to learn a lot. If I can't handle it by myself, I
will give my wax prints to a shop.
TIA
Nick
PS: Small fittings will be made spinncasted in zinc. Thanks for the
tips/links I got that for!