I have done some research on the site but can not find out whether a 454 with a th 400 will fit in a 65 chevelle. Any help will greatly be appreciated. Thanks.

Both with fit. You will need to change the engine mount brackets to fit a 454 BB. A 400 SBC will bolt right in.

Actually, the small block frame stands are the same height as the big blocks. The only difference I've seen is that the big block mounts are shaped differently on top to clear the interlocking tab of the factory style big block motor mounts. If you use a pair if Energy Suspension mounts either frame stand will work. I've done this swap twice, send me a PM if you want more info.