I think you're going to lose a lot of the beer to the dry hops, that's the advantage of the oil.
Plus the oil will provide a much more intense aroma, like the BIPA had, and without the grassy tastes that whole hops can add. Ballantine used both dry hopping and hop oil. You can skip the oil, but not if you're looking to recreate the original product. Those who never tasted the original probably wouldn't miss it. But I drank so much of this stuff back in the day that to me, it would be the missing link.
There are different types of hop oil, so it's important to get (or attempt to make) the proper type...there are specific oils made for bittering, for 'late hop' flavor, and strictly for aroma. Ballantine made their own, and unfortunately none of the former Bally workers I talked to could supply any specifics on the setup or methods used to extract and distill. I'm guessing that there was ethanol involved for extraction which was then redistilled, most likely under a vacuum (thus allowing far lower evaporation temperature and less damage to the aromatics). But that's just speculation.
As far as the aging, I agree that 20 years for the Burton isn't very practical for hombrewing unless you're ambitious and start young! (my Burton gets an average of 1 or 2 years and I'm pretty satisfied with that.)
But that one year that was part of BIPA's production isn't hard to do on a homebrew level. The long aging is a very important aspect to consider when trying to re-create this beer.