I have the usual old rustproofing scale and flaking going on.  I can deal with that using carpenter wood chisels.  They are sharp enough to knock it loose.  My question is the remaining light rust on the major frame crossmembers.  How have you all dealth with that without frame off restoration?  Any tips, ideas or suggestions are welcomed.  Odly enough on the front suspension major components where grease lubrication was a maintenance requirement, there is little evidence of frame rust, probably because of the close proximity of all the grease fittings.  Go figure.  Thanks, Charlie.

As long as it's just surface rust, I would sand it off, coat bare metal with a product like Rustoleum Rust Reformer, and then top coat. 

My car was undercoated 50 years ago, if not more. I don't know if it's factory or aftermarket. I will say that being undercoated, and having spent its entire life in California, there was very little rust. I did find some minor surface rust on the interior-side of the floor pans, in the foot wells, but you won't find any now. Removing the undercoating is a messy, labor-intensive job, so I'm leaving it. Unless you are doing a body-off, rotisserie restoration, I would only address those areas that are flaking off.  

Don't forget about the inside of the frame. That's where the real rust happens. Use Cavity Coat or similar lanolin product with a long tube attachment.

"FREE SAMPLE"

lord is right,the last 55 i did frame off the curb in frame for rear axel was full of mud and when cleaned i had to cut  out sections of the curv and replace part of the outer frame,same both sides.,of the car,. the inner sides seemed ok.
with both doors off i made ties frame door hinges to striker plat se kept the body from bending. rolled frame out from the body. also found some damage where the bumper(rear attached.. rest of frame was sound,thanks to rear seal and pan oil leakes.