mate, what brake master cylinder are you using? i assume you've measured it up with the engine in the bay - there certainly isn't much room behind the inlet manifold in my ke20. i have the same motor as you with a cut n' shut manifold.
i have an rx7 dual circuit master cylinder, only the fronts (ke55 solid discs) have the booster (vh44) and my engineer was amazed at how well it stopped.