I don't have an answer for you and am holding back my strong desire to flame you (I have a '70 Bee post car so please understand). I would say this...

They made 1/4 or so of the post cars as they did hard tops. The post cars are often worth a touch more since they are more rare (and the slightly stiffer chassis holds up better to years of high torque pounding). See if you can sell your post car and buy what it is that you want rather than modifying the more desirable car. There may be someone out there really looking to find a post car.