If I had to design one, it would have to eliminate the hump it has just before the inlet ports, for starters. Then, I would create a larger volume throttle chamber, while using a larger throttle body. Maybe a Honda with built in map sensor.
I'd maybe use a Miata or JDM base with a custom plenum.
I would switch to a larger TB - but not too big, the larger the TB the less linear response you get. It becomes more of an on/off switch.
Stock TB size is 50mm. Maybe an aftermarket Honduh unit (cheap) that's 60 or so mm in dia
The OE throttle body on my 91 Isuzu Impulse (also a 1.6L turbo dohc) is 62mm if I remember right. It made ~160hp, factory, with a slightly larger turbo than the Capri (i believe it's equivalent to the VJ11)
I believe I've read optimal plenum size is 1.5x engine displacement. But I would recommend further research on this before diving down that rabbit hole. There are a LOT of dynamics at play in intake manifold design.