Re the question from 127 - it doesn't matter whether you pre or post flash. The results are the same.
Flashing adds a small, uniform amount of exposure to the entire print. In the shadows, this amount of additional exposure is trivial compared with the blast of light through the clear areas of the negative, and so the amount of increased density in the print due to flashing is negligible. But in the highlights, which are the areas of the negative with the greatest density, the incremental flashing exposure is more significant and results in a perceptable amount of increased tonality.
Flashing is an experimental process - the amount to do depends on the amount of contrast reduction you are seeking and the way you go about doing it. It's relatively easy to get a decrease in contrast of a quarter grade or thereabouts.
I do it using a flashing card. This is a sheet of heavy cardboard with a large (about 8x10") opening cut into it. I glued a sheet of drafting film onto the cardboard. After I have made the base exposure and done whatever burning I feel appropriate, I slip the cardboard under the enlarge and give the print an additional bit of exposure through the drafting film while jiggling the flashing card. Note that this approach does not require a second enlarger, an auxiliary light source, or that the negative be removed from the enlarger. The image-bearing light from the enlarge passes through the drafting film which acts as the mother of all diffusers, completly obliterating the image and producing instead pure light on the easel. It also absorbs quite a bit of light. I find that a flashing exposure of about 5 - 7% of the base exposure is the ballpark necessary to reduce contrast a bit and give a little texture to marginally blown out highlights.