Diamond Jim wrote:WA is different. I seriously doubt WAPOL would allow a conversion kit or anything like a shoulder stock that effectively creates a short barrelled rifle. An email to WAPOL would give you the definitive answer.
Yes, WA is very likely entirely down to what the Police allow, regardless of whether it complies with or breaches the actual laws. I would think the chassis itself is probably unregulated but combining it with a handgun may well create an illegal situation. If nothing else, it very likely makes the firearm no longer eligible for whatever competition you used as your genuine need to own it.