why don´t you search for directly for 16VT piston? .. I think that companies like Woessner, CP, maybe JE make ones and from woesneer are the cheapest you can get (and together with rods, which you will also need for such BHP level..)
20VT pistons can fit - if you order oversized ones (to 84m), but you will need longer rod and probably machine new cut-outs for valves, as 16VT has bigger valves than 20VT, and even under different angles....
just 5 seconds of google search :
https://www.gazzellaracing.com/product.php?productid=19874&cat=3762&page=1 (and you can built simmilar/same set cheaper..if you will ask more suppliers of performance parts..)
