Thank you for a quick answer.
I believe basing the Susi so directly on the Pasi is a bit... optimistic.
I'll give you some background. The entity that designs and builds the Susi is the post-War *Valmet, a combination of previously mostly private companies taken over by the Finnish Emergency Cabinet in 1984 and after it. The Susi is a product of the "State Machine Factory, Pieksämäki" (Valtion Konepaja Pieksämäki or VKPP) that is built around the State Railways maintenance facilities and workshops in Pieksämäki in the post-War years. The VKPP is the main actor in keeping the Finnish state's military vehicles running, and has in the two decades after the War been basically rebuilding, jury-rigging and cannibalizing various vehicles (pre-War Finnish military and civilian cars and trucks, captured Soviet vehicles, etc) to keep as many as possible running to suit the needs of the nation (as understood by the military government).
By 2000, though, many vehicles are getting worn out. And there were not that many wheeled APCs that survived the War in the first place. Only a very few of the first generation XA-180s that had just been built prior to the Exchange would have been left after 1984, and only a few of the people who worked with the project besides. The FNA military police has been using a handful of BTR-60s (some of them ones the Finns captured from a Soviet remnant in Finland) as its first line "showcase vehicles" to present a mighty front to the population.
Now even the BTRs are getting difficult to keep running. The FNA is all about appearance, and the fact that the Finnish military is ITTL by the year 2000 mostly down to using repurposed civilian cars in matte green (or black-grey in case of the military police) annoys the military leadership.The Susi is seen as the new, modern vehicle to bolster the military police's prestige and appearance. Built on a chassis purchased from the Czecho-Slovaks, who by 2000 or so have some vehicle-manufacturing going again, and made partly by hand at the VKPP. Put together with the resources of an impoverished military state, it will use some parts salvaged from older vehicles, out of necessity.
In other words, the Susi is a semi-improvised vehicle that wants desperately to look
not improvised at all, built for a failing state that needs to look strong to keep going. I mentioned the Saxon before as I think it looks "improvised" in the way I imagine the Susi would be - somewhat non-symmetric, with odd angles here and there. The BTR-60 would also have an effect on the design as it is what the VKPP people are familiar with. Some inspiration could also be found from the PanssariValmet, a OTL Valmet-made APC built hurriedly on a tractor chassis at the time the Pasi was being developed.
The PaVa:
Or see
here.
A Saxon in use by the Ukrainian military, very much akin to how I see the Susi: