The accessory holes was a good comment. Not sure which heads don't have them any more? My old B1-B/S (from the 1990's) heads did not have the accessory holes drilled.
Need to figure which heads will work with your combination first, then look at price difference between new and used, and what comes with each.
If the used heads come with rocker arms, that would add another price point, and something else to check over.
As mention, if the heads have been milled, it could mess with the intake manifold alignment.
If you plan to use a power adder, you may want upgraded valves and valve seats that handle higher cylinder temps better.