You have a very interesting project with a unique choice of engine. The original OS Giken engines are extremely rare.
Coincidentally, I'm building a few S30 and KPGC10 models for a contest in October, and Z432 and Skylines need a new S20 cam cover because Fujimi part looks too wide. I'm also making a special L24 engine for a custom S30.
Looking forward to your progress.