Build-a-dash!
Judging by the looks of things ....you have screen all over the front side of the dash. you should REALLY remove the gauge cluster and heater controls.
as mentioned above, grab a steering wheel puller and it should pop right off.
then lean under the column and loosen the support bolts that hold the column up and you can get it to drop 3 or so inches and gain some extra room.
the glass really should be out so you can get to everything good.
if I were doing the top of the dash I would probably layed something down first like seran wrap or something so that I could mold my body filler to the dash but yet also make it removable and then you could have attached it in some way rather it be by screws or velcro or whatever.....reason being, the body filler will be exposed to direct sunlight,heat,vibrations and so on and it will probably eventually crack and then you will have to go through this hole process again.
it would have been a cheap and easy fix to get a new dash pad ( I actually just seen a member had one on here for sale for really cheap).
but its always cool to have a car that stands out and is a little different too!
there are a few threads on here of guys who have smoothed there dash's over (most welded in patches over any holes in the metal) though. you could probably do a search on them and you might see a few cool ideas for your project.
good luck and remember ....if its worth doing....its worth doing right, so take your time to make a good plan and to round up the right tools and to go about it the right way and then jump after it!