First I am not aware of any 4 door convertibles for that year.
Second yes if you have the money and time it can be done. I have not done one but there are some things you will need to be aware of.
1) You will need to reinforce the lower body BEFORE you cut out the B-piller. The body uses the B-piller for support, cutting the piller before you reinforce it will cause the body to try and fold, which will shift things out of alignment. You will have to add some heavy metal to the rocker panels, coming from the A-piller all the way back to the C-piller.
2) The roof will need a little beefing up as well.
3) What is left of the B-piller will need to be stregthened inorder to support the door, and not have a tendancy to sway in-and-out.
4) Your doors and windows then will have to be custom modified inorder to close and seal up properly.