The Catalyst 3750E can be stacked with the Catalyst 3750.
The 3750 must support the global features (Interdependent feature) already configured in running Configuration on the 3750E stack (eg MTU).
Newer 3750E port features can only be configured on 3750E ports and newer 3750E global features cannot be configured at all.
Power down the switch you will replace and as long as you do not segment the stack (deliberately or accidentally making them two separate stack) it should be fine.