Mouse Wheel Scroll In A Combobox On Userform (Lots Of Code)

I have seen some code around that allows scrolling in listboxes using the mousewheel. I have also seen some code here on the forums about scrolling through a combobox embedded in a workbook. I have tried adapting both of these to suit a combobox on a userform but I cannot get either to work.

Here is the code that I used for the embedded combobox; I added it to the base code for the userform

I then added the following code to a standard module as stated in the forum post;

In the first section of the code there is a msgbox that never gets shown so I don't think code is recognizing the mouse wheel at all.

The second set of code that I used was set up to work with a listbox and it works perfectly with a listbox control. The problem is I cannot adapt it to suit a combobox and if I use a breakpoint to see what is happening Excel freezes.
The following code is added to the userforms code;

Then in a standard module I added the following code;

I added this section of the code;

I think this should only work on a Combobox but a Combobox does not appear to support the TopIndex value. Is there a way this can be setup to work with a userform combobox?
Sorry about the huge amount of code.