Sure, that would be the absolute best IF you can get the engine back far enough, but for most here aren't going to able to do that. Not to mention that you will have to do something to clear the rack/pinion.
I moved my front suspension forward about 3.5 - 4", and in the future I might be able to get the engine back about an inch or so.
I disagree about 100lbs of ballast as that really isn't huge weight, and I don't mean to put it right on the rear bumper, but somewhere low, behind the drivers seat. Maybe a bit more on the rear passenger side to off set the weight of the driver
I was thinking in slightly smaller terms...but yes, moving the engine back would be an amazing improvement.
You have definitely made some huge gains if you've already moved the front axle center line 3.5" - 4" forward!
As for the weight...I was just going off of personal experience...&, you must have a lot more H.P. than me.
My suggestion would be to start with 25lbs & move up in 25b increments...if you can, on the scales first, then out on track.
I must have misunderstood you as to where you intended to place the weight.
On three of my track cars we played with moving the battery (approx 48lbs) around that approximate location, while the cars were on the scales...all the cars had factory front axle C.L. locations.
In the first car, the best result on the scales (with driver in the car & 1/2 tank of fuel), came from placing the battery in the front passenger side seat location, towards the rear mounting holes of the seat.
On that car we left it in that location until we finished testing & decided to install a passenger seat. We moved the battery to the rear passenger side seat location because of clearance issues. There was a felt difference in sharp left transitions when we moved the battery (probably due to the weight being moved up as well as being moved rearward). That difference was muted a bit when we had a passenger in the car, but the passenger also changed all the handling, acceleration & braking dynamics.
With your modified front axle C.L. location, the front passenger side seat location might work even better for you! Only the scales & testing will tell.
All the other cars were mostly street driven & had passenger seats...so the rear passenger side seat has become my default battery mount location.
In your case, placing your ballast around these areas might help.