Ideally you need someone thats familiar with K-jetronic fuel injection to tune it.

They only had 150 hp when new

There's a Maha dyno in Wisbech ran by a Father & Son team called Maxtreme, they do a lot of remaps on newer stuff - whether they know anything about older stuff like the XR4i might be worth asking. https://www.facebook.com/Maxtremetuning/