When I looked at that route, I decided on scrapping almost everything except the transformers, chassis, and the rectifier. I decided I did not want to have to hunt bad passive parts when new ones cost nothing. I did not want to fiddle with desoldering tube sockets when new ones cost $3, and I did not want scratchy pots, sockets and switches when new ones cost so little.
I enjoy a good rat-rod build as much as the next guy. Experience has taught me that except for the chassis, transformers and possibly tubes everything else is gutted and replaced with new components. Amp builds can be buggy enough without having to chase down arcing tube sockets or worn out pots and switches.
*the above amp is a 5E3 Deluxe built into an old Hammond AO-35.