I found a photo of an original HSE and veneering it would be a difficult project. Design wise the top cap would just have to go but the rounded corners stay, they are helpful in controlling diffraction.
If you can live without the grill cloth then a gloss paint job would look great. As long as you have the drivers removed you can glue in slabs of
Richlite, this stuff really works wonders tightening up bass and focus. Richlite costs $25/sq ft. and you would need 5-10 square feet depending on brace layout, I got free cutoffs from our neighborhood retailer. Playing with the stuffing is easy without the grill cloth in the way, it took me about 4 trials until I got the right amount of Kapok installed in each speaker.
Wayne