looking strong, page-126

For passive (index) fund managers I can't see a competitive advantage by keeping the stocks they have in their portfolio secret so they should be fairly transparent. The only thing I can think of is that S&P who from memory created the S&P ASX300 Index might have some licensing restrictions which may stop the fund manager from sharing some of that information with you.

I was told by a past colleague in the industry that fund managers are not obliged to hold all the stocks in the index, however there is strong emphasis to match the performance with minimal of variance between the index and the fund performance. Looking at the Vanguard website, it does confirm that for the ASX300, they only hold 290 stocks, so they could exclude ten ASX300 stocks based on criteria their investment team set.
Matching the index performance would be difficult if you have a stock like ADO which has experienced some volatility even if the weighting for ADO would be likely to be quite small.

In relation to your question. Assuming you get a breakdown of the stocks, their weighting and you find that this is different from the index for some of the smaller stocks like ADO, unfortunately as a retail investor it would be quite surprising if you could influence their portfolio allocation.