A quick flick through the RD wikipedia page gives us some food for thought from OTL.
https://en.wikipedia.org/wiki/Roger_Douglas
In February 1983, when Lange became leader of the Labour Party, he made Douglas the Labour spokesperson for finance.
At the time of his appointment, Douglas had a reputation as a radical but his thinking on economic issues remained within the boundaries of Labour's Keynesian approach to economic management.[23] By the end of 1983, his thinking had shifted markedly to the economic right.[24]
These observations came from Brian Easton's 1989 book about Rogernomics. However from the man himself (RD) we get....
Douglas’s insistence that economic policy was the product of a plan conceived by him as early as 1980[39]and not a response to crisis left the government open to charges of bad faith.[40]
According to RD, OTL 1984 budget was conceived by him as early as 1980.
So the capacity for ATL Rogernomics in '81 is there, but without OTL 1984 financial crisis it there would be less political scope for more radical elements of the policy.
Another interesting issue is the politics around the New Zealand Dollar.
In OTL, the Labour Government elected in July 1984, devalued a the NZD by 20% soon after coming into office and floated the NZD in March 1985. All this was done in the honeymoon period after coming into office after sustained selling pressure from financial markets. Muldoon was steadfast in holding the value of NZD against these pressures which built up over time.
In an ATL '81 Lange Labour Government (LLG), this would have gone quite differently. In OTL Douglas did not believe in floating NZD until the end of '84. As finance minister in the ATL '81 LLG he would he progressively devalued the dollar by 5 or 7.5% increments. When Governments set the value of the currency they were pitted against financial markets in a battle of wills as to whether the Government would blink against the currency traders.
An '81 LLG which would have been elected with a small majority would have suffered if it devalued the NZD several times in 83/84, could have very well lost office. Free market reforms would have become the preserve of a National Govt elected in 1984.