Basically, the answers to your questions have been answered- and answered over the years.
One was very recent here when I mentioned Turciting the saddle. The reason- or one of the reasons is to compensate for the possible misalignment of the leadscrew when a marked reduction in thickness of the bed is created by scraping. However, you will almost certainly hit the problem of having to compensate for the saddle which will be worn as was the bed. You are going to have do both together. Whether you pad the saddle with metal or turcite or use a liquid plastic is obviously your choice.
So moving back to the bed, you will certainly have severe wear on number 1 shear about 6" from where the chuck should go. You'll have to correct this before playing with narrow and whatever guides.
What you should find( I've done several beds) is that number 4 shear is an 'air fit' and has never been used in anger. I've found mill marks here. So you can bear off Number 4 to correct number 1!
As for the central gib, all the experts on Myford have hit problems because the inner guide on the saddle assumes a convex curve. So you can choose your correction to either Jack Radford's methods or Martin Cleeve's. My take is that it is a lot easier to add an adjusting gib to bear on number 4 shear than scrape and or build up the inner guide- which if you think about it will have a worn shear.
And that, basically, is that.
Norman
