Fitting Interstate tank to a 1970 Roadster

Hi, has anyone fitted an Interstate tank to a 1970 Roadster or a S type 750.

I have offered up the tank but the side panels stop the tank fitting properly. I have a picture of the bike from 1982 and it appears that the side panels had the top corner cut off.I have a spare Interstate tank that I could cut the bottoms off, but a bit drastic and I also have a spare pair of S type side panels I could cut, again a bit drastic.

Is there another larger capacity tank I could use or are there another type of side panels that would fit.I have a central oil tank and it seems that the Interstate side panels bolt onto the oil tank which I  can't do,also the ignition switch is mounted inside the lefthand side panel, any suggestions, regards, Dean.