No, the two are not equivalent. In the first case, the investment in this period only adds to the capital stock next period, while in the second case, it adds to the capital stock right now.
Two additional remarks:
The economic meaning would still depend on how capital is used in the rest of the model
In Dynare, the first case would have a different interpretation, because the X(+1) actually means E_t(X_{t+1}).
The two timing conventions are equivalent if you use the predetermined_variables-command. See the manual
Sorry, but this is a problem you need to solve on your own. You are the only person who knows what the 40 variables are and which equations are involved in the model.