This is a very generic question that really has no answer. The "best" will vary depending on what your intended use is so there is no one answer to that. Anything made for an itr will fit.
You should do forged internals IMO, do it right the first time. LS isn't a bad choice and will probably be more cost effective. Add some fuel and ignition to the above and S300 and you'll be good to go
Don't get upset, I was just pointing that out in case the individual you were suggesting this to was unaware of their poor status. Plus if its a bad idea it's generally smart to not include the option in the first place :twocents: