Has anyone ever drilled and tapped a hole on the top side of this type of cover or maybe welded a fitting or bung so it can be used on a wedge with motor mounts?

Like this .

Exactly. The 21215 covers are not readily available, so instead of having to spend the $400 on the 21815 pump and $200 on the longer shaft, and just use the stock cover, I began to ponder. The material is pretty thin but if you could just catch the backside of the current hole you could possible have enough to keep it tight. Again just wanted to see if anyone had tried it.

I thought the cover hole was for the wedge and back hole was for Hemi, then again I might have em backwards? Both of mine have both holes.

Drilling and tapping the end is no problem. Make sure you tap it with an NPT tap. If you tap it with a standard tap you'll have a hell of a time getting it to seal and it won't leak but it will suck air.

EDIT: If you use the existing fitting then you can just tap the hole with a standard tap - that fitting seals with an o-ring.

You're right. And the cover the OP has is for a hemi.

I've made a lot of different pump covers. This style was my favorite for awhile.

that damned thing almost killed me! The green gasket blew out because the bolts aren't centered properly, and it blew at 153 mph in the traps at RockFalks Raceway in 2004. It instantly oiled the left slick, sending me sideways. The good Lord helped me save it from a crash, but to do so is virtually unheard of as far out of shape as the car was. Milodon makes a couple of different covers without that gasket. They no longer make that thing you have for a reason.
EDIT
sorry for coming across so strong, i just don't want anyone to be hurt by that bad design. I remember going to extra effort to make sure the bolts were tight. The gasket just blew a chunk out on rhe side with poor support. I have that failed gasket hanging in my shop as a reminder .

I wouldn't do that, that early cover is to thin How about using a 90 degree hose end on that fitting to get around the wedge mount? Or maybe use a Elephant ear or a front motor plate and remove the stock driver side motor mounts so you can use that cover

This is a one-piece cast aluminum unit made by Muscle Motors. They were $100 when I bought it a number of years ago. Rather than dick around with the one you have it might be worth a call to them to see if they still have any.

They work good! That'a the one I have on my 64...

yes i see that "green gasket " in there ....get rid of it. Best option is to unbolt the filter adapter, tap the two holes and plumb a remote filter. Makes for a lot safer setup , no chance of oil down/gasket failure

You could probably message Jack Moore ( Moore and Moore racing) in Ohio and he could probably sell you one. He always had these for sale

That is what I did many moons ago.

What are you guys making the new gasket out of?

Why not check on getting it o-ringed. I never had the green gasket break out but chit happens.