I disagree that they all steer hard ... after I finally rebuilt the box in my 59, it steered just as sweet as any non-power car I've ever driven (and better than some). Did still have a bit of play on-center, but that was because I chose not to replace the worm. New peg, bushing, seal and a couple of shims; whole project cost less than $50 and I felt a fool for not having done it sooner! I could easily park with one hand, and change lanes on the freeway with one finger. And that was with wide, sticky tires.
I've not driven the 57 yet, but it's easy to steer around the garage with just one hand.
I believe careful adjustment is key. The first tip is to get a dial indicator with magnetic base for checking the end play. Add shims as necessary to get some end play, then measure it and remove exactly that many shims to get zero end play. Although the book notes that some pre-load is permissible, it will cause hard steering and so it's better to make it as small as possible. As I recall, you can get within .001" by mixing shims and gaskets. Also be sure the peg cannot interfere with the endplay measurement; either back the peg adjustment off or remove the top plate while doing the end adjustment. The end adjustment has to be done first.
Then to adjust the peg properly, you must have the box disconnected from the steering. You should be able to easily turn the bare shaft with your fingers (but be careful not to let it slam against the end of rotation, as that can damage it). Proper adjustment is when you can just feel the tight spot in the center. Note that position, as you should use that as the center position when reassembling the steering.
A good lubricant also makes a big difference, IMO. I use Valvoline full synthetic gear oil.
Hardest part of rebuilding the box for me was getting the Pitman arm off the rocker shaft. Lacking a proper Pitman arm puller, I tried to make do with my 2-arm gear puller. Had to add supports to keep the arms from slipping off, and then it was adequate, barely. After that, everything else was easy. I used flat washers and threaded rod to pull the bushing and seal; then reversed the process to install the bushing. The seal just taps in. The book says the bushing needs to be reamed, but mine fit perfectly without reaming.
Alignment is also crucial, especially with the split column. I suggest installing all of the fasteners loosely (including the pinch bolts that lock the box to it's bracket and the bolts that hold the bracket to the frame), then first tightening the pinch bolts that hold the columns together. After that, wiggle everything and check for free steering before starting to snug up all the other bolts.
And of course check for binding throughout the remainder of the steering. Herman wrote of finding bent vertical links on his TR250; and the idler arm on my 57 was so stiff that I had to use a hammer to unscrew it.
Don't forget that felt bushing at the top of the steering column either, as it has to take any side force applied to the steering wheel. A healthy dose of powdered MoS2 (aka moly aka molybdenum disulphide) will help it out.
The 59 had the brass/stainless replacements for the silentblocs. I selected those just because I was tired of having to replace silentblocs every few years, but they may also have contributed to the easy steering. I moved them over to the 57 while I had it apart. If you use either these or the (less expensive) Delrin ones, be sure that the idler arm lines up with the steering box. If you just let the idler droop on it's bolts while you tighten them, the hard pivots will bind.
AFAIK, all of the R&P conversions lose the self-canceling function of the turn signals. The most common solution is to convert to a MGA turn signal switch mounted on the dash, which has a pneumatic time delay built into the switch. But others have just foregone the self-canceling feature.