No downside really. HQ to WB were all pretty much the same chassis apart from RTS being added.

Back in the 80's in Brisbane a mate of mine hit a horse in his HZ sedan and bent the front chassis rails, we went to the local wreckers and got a set of rails off a HQ sedan and bolted them up and repainted the car while we were at it. The car ran out of rego during the rebuild so he had to get a roadworthy for it and present it to Qld transport for inspection.... It got re-registered as a HQ because of the chassis so out came the 202 and in went a 350..... all legal.