Great work Haydn.
As I'm sure you've seen the castings on the intake and exhaust sides of these engines is far from perfect, if you can smooth things out a little and remove some of the flash and casting marks it will really help airflow. I'm sure you're aware that you need to be careful not to make the intake side of things too smooth, you need to retain some level of turbulence within the intake for efficient combustion, if its too smooth you'll actually lose power. The exhaust side of things needs to be as smooth as possible to allow gases to escape quickly. Its a really labour intensive process but worth having a go at yourself as its very expensive to have done professionally.
This guy in Malta is restoring a Biturbo Spyder (2.8 18v) and his videos are very interesting (if you like Biturbos
), this particular video might be of some use for the port grinding process, it mainly concentrates on the exhuast side of things but he does cover the intake manifold somewhere:
https://www.youtube.com/watch?v=PI4sjez3c28