Iv had the hks bov for about a year now, it should be very simple to fit only took me about 25 mins, the instructions are in japanese but if you take a good look at the pictures then you should be able to work out what you need to do. I am assuming you have the specific valve with fitting kit for the supra? if so everything you need is in with the kit, it goes in where the existing valve is, you wont need to do anything with the engine setup or turbos.
some people have these welded onto the IC intake piping i am not sure what the pros/cons of doing this are?
I can post a picture of mine fitted if it helpes.