An 85 GN has what is called a "hot air" motor, which means that it is NOT intercooled.....These motors are not as fast as the intercooled ones, and those that are, usually requires a good amount of money.....It's going to be asked of you so I will skip the drama and ask you now......"How fast can you AFFORD to go?" If you are looking for a daily driver 11 sec GN, my advice would be to pull the engine and start looking for a good shortblock on this board....or a block and start the build up yourself.....Also you need to start researching and learning the nuances about these cars.....
Turbo Regal Web Site is an excellent place to start......You also need to start knowing the differences between the hot air motors and the intercooled motors, because the differences extend to more than just intercoolers.....the opinions will vary, some say the webbing in the valley of a hot air block is weaker and therefore does not lend itself to living up to very low second times.....(9's, 10's etc) but if you are building a pure street car, there won't be any point of going nine or ten seconds either.....To make an extremely long story short......it all amounts to one thing you need to get started on..
Research..
I hope this helps and good luck
Steve Chambers