Hi all I want to say I am in heaven there is an impala site! Question I am trying to purchase a 67 impala but it has post on doors. How hard is it to convert to postless hardtop like the one n supernatural?
The two door hard top is basically a convertible with the top stuck up. It is an entirely different car with the exception of the front dog house being the same on all models in that year. It has a different frame and cross-members , doors roof rear quarters, trunk rear facia. Dash and cowl are the same as well as the toe boards and I suspect the floor boards could probably be reworked to interchange but I believe they are different. Dash is the same under the trim and possibly most of the trunk pan as well.
I saw Red Green do it on this show once. Only took half an hour and six rolls of duct tape.
There have been a few similar questions asked and the usual response is that the work is not worth the effort plus you will compromise safety by removing the center post. I did see a picture of one converted but it looks wrong, the roof line is not the same. The main issues are structural and window/doors. I would suggest just removing the chrome trim surrounding the door frames and painting them black to try and hide them. It's simple and most people will not know the diffence unless you park next to the real thing.
Like Craig said the car body is stressed member. It isn't as stressed as it is on a uni-body like a Camaro, but the frame is different between a sedan and a hard top. The frame is stronger on a hard top than it is on a sedan because the sedan has a stronger roof to distribute the stresses (for this reason a sedan is lighter and stronger than a hard top, which is why racers choose a sedan to make race cars out of them). If you cut out the sedan door posts and cut back the rear sail panel out to emulate the hard top roof line you risk the car breaking in half. It can be done; as can converting a four door car into a two door (as used to be done before shoe box Chevy's where reproduced to remove the incentive with brand new 1955-'57 Chevy's being made) but the ends do not justify the means as there are still four door hard tops around to buy.
The rear doors also attach to the post between the front and rear doors. If you turn it into a hardtop, much reinforcing would also be necessary in this area. This is absolutely not worth the trouble though.
Would it be better to put the 67 sedan body onto a 68 hardtop frame then switch out the doors and roof? I know the hinges are different for the doors but that's an easy fix. But would it be better that way since it will already have the needed suport in the frame so it won't need added support?