would this fit the R

I know people have done it fine but I wouldn't be bothering with a Silvia etc manifold.

I've never considered having it ported. I was under the car searching for a leak the other day and noticed that the manifold has really seen better days.. how much is it to port? What are the gains if any? Smoother flow.. still need to heat wrap a few things

Weve done a fair few of them now and definately increases the gas flow over the rough cast stock item.
Open the ports up around 2mm and match head ports (without going right into the main gallery of head) You will find that carbon deposits dont build up as much either.
Combined with a free flow elbow youll get faster spool up time and also if you have larger duration cams fitted youll get the best from those too

Yep port standard best you can (weld fill recess for max port work) and blast it clean and do a real neat job with some charcoal black heat wrap then add a quality elbow and they will do over 450hp and look decent under bonnet too plus don't crack or fall off or sound like a bees nest like the cheap stainless shite .

I'm making outside of ports tad bigger  ( usually by 2mm nor much more) but I do lower the floor between cylinder 2 and 3 and I weld recess on the collector and grind it smooth inside. Also I smooth it with something like 120 grid emery cloth... I take for it £50 ( and obviously delivery).

It looks like that 


https://youtu.be/hnIclr8ddno