re foam question

I have a pair of vintage large advents that I need to re foam. I have done one pair, but that pair had the metal basket ( sold em' not as good) This pair has the masonite woofer and looking at them , its going to be completely different job. Doesn't look like you can remove the masonite (glued in) How do I do these?
Parts Express sells masonite woofer surrounds. These get glued in with the roll facing INWARD. You first glue the inner edge of the surroud to the top of the flat edged cone. Push the surround in so the outer edge of it is below the masonite. Let dry. Then, apply glue to the outer edge of the surround and apply a DC voltage to lift and CENTER the cone and VC in the air gap. With the surround up against the back side of the masonite apply pressure all around until the glue sets.
DO NOT remove the masonite to do this job!
For a more precise job, remove the dust cap and use shims.
Thanks for the response