Prices fall out in the wash. Investment is not constrained by savings, but savings adjusts to the investment decisions of capitalists. Consumption per head is known given the technique and the rate of growth. This is a debated point. Whatever it may be, it cannot be equated with marginalism.
Marginal techniques are the common possession of all theoretical economists.
The theory of intertemporal equilibrium is commonly thought to provide the Neoclassical theory. Consider an economy in equilibrium at a single point of time in the sense that all markets clear. All markets are barter and all transactions planned for forever are contracted for at this single moment. In other words, all possible future markets exist. The initial endowment is given and individuals must make decisions trading leisure for goods at various times and consumption decisions across time.