PI inlet manifold ?

[Trolleybus]

I have just had another look at a set of 2.5 PI inlet manifolds I purchased to convert to a single throttle set up for my EFI project.
The manifolds are just too good to chop up so am looking at making some.
The 2.5 PI units have a tapered bore ending in an off round ovaloid hole at the head end.
The question is why is the exit hole this shape?

[GT6 M]

the shape was like that cos they found tht this shape introduced a bit of swirl
t,mixture, an also, the idle air pipe is at front, so idle air will mix wid fuel spray after its injected, no befoer like the earlier,ns

alledgedly they were cast in perspex,so to see air flow
or so I read some where yonks ago

butt a few questionee,s for ye
1, why have they got to be chopped up
2 wots up with the OE linkage,

granted there a merits an demerits of both set ups, but if a bit of attentionee is med to the linkage, then its a decent set up.

M