I had mine up on blocks last week with all the wheels off for a poke around looking for things to fix. I’ve done near 7k miles in a year and a half of all weather, (but mostly dry), driving.
There are no signs whatsoever of any chassis corrosion, the under seal is very thorough.
I have a tin of black waxoyl for brush touch up, the cross rail under the gear box has been scraped a few times and an aerosol of clear wax for bits I don’t want covered up. I actually took some of the black off my shocks and springs and sprayed them with clear, I like to see the colours

The ARP4 with the red chassis would be my next on the list, it would be a cleaning fiends dream!
The only rusty bits were the unpainted parts of the front hubs, not any more though.
I really wouldn’t worry, get it ordered and find some roads where nobody goes.