F-Max and Turbonetics carries manifolds that work with T3 turbines. I think there is a recent post somewhere that may have had a few others. The Turbonetics mani is the revhard mani. I think Turbonetics bought out revhard, but don't quote me on it. It's just what I heard and a turbonetics rep did tell me at SEMA it is the rev-hard mani that it in their catalog. The revhard mani may have fitment issues in the 240sx with a T3 turbine as it locates it very close to the brake master cylinder. The T04 on-center turbine clears much better.
The F-Max mani is log-style and fits very low as it mounts sideways, where as the Revhard is a top-mount. You may be able to get the revhard mani cheaper through NSport or XS Engineering as well.
http://www.f-max.comhttp://www.turboneticsinc.com
As far as being out of a Starion, I don't know the specs. If you can find them, I'd be happy to look at the compressor map and tell you what I think. But even then, Personally, I would go bigger.
Not sure about the cams. I speculate that it may move the torque peak up to a higher RPM, but there may be a little more overlap. If there is, the turbo may just push some of the air through the motor and out the exhaust. A little bit of this is fine, but too much and you'll end up working against your turbo to a small extent.