Getting scaling accurate requires math, and is easiest done with brewing software.
There are two most core efficiencies. One matters for scaling, the other does not.
Mash/lauter efficiency- the efficiency of getting wort sugars into the kettle- is the important one. This is what you need to scale to.
Brewhouse efficiency is what makes it into the fermenter, and takes the above but factors in losses. It has no impact on the character of the beer that isn't already factored into the above. And EVERY system will be different.
Losses can be different. Volumes might be adjusted accordingly to account. You don't use their system, so why try to account for them.
So what do you do?
Don't worry about the grain weights. Look at the *percentages*. Ex: 82% 2 row, 8.5% Crystal 60L, 4% Black Malt, 5% flaked oats.
Keep those percentages. And scale the weights so that on *your* system you hit gravity and *your* preboil volume.
THEN, scale the hop additions proportionaly to your system. I like to keep late hops (20 mins left or later) factored by an oz/gal or lb/bbl ratio, even if alpha acids of the hops change. Then I will adjust the *bittering* hops based based on my system to factor both any change in hops alphas (late hops included) as well as boil volume/boiloff changes, so that I match the IBUs.
Say they're listing a 14.5%AA Citra with 1 oz each at 60 mins, 10 mins, flameout, and hopstand, but the Citra you get is 13%AA. Assuming the same "batch size" (you unfortunately do have to make assumptions here), you'd keep the 10, flameout, and hopstand 1 oz additions, but you'd probably have to imcrease the 60 minute to match the IBUs.
Even if you get the same %AA hops, I'd still calculate the bittering additon out with your system- changes in pre boil volume and boiloff rate will change the alpha acid isomerization.
Using this, you can scale not only for efficiency but for batch size as well.