The RSO is old but at least an interesting variant but the PAK40 just has to go. Upgrading the tracks would be an obvious improvement, as would raiding the Dragon kit if you have one for extra parts. I do it all the time as an easy upgrade. On a silly dare I recently did just that with the original 1969 release Tamiya Tiger I -there wasn't much left after it absorbed a god part of my spares box. Yes, it was a silly dare but hey, we are building models, right?