tclederman, on detent springs and balls, don't sweat those balls nor your own. You will not need new detent balls. Only exception is when you are working with a totally rusted out transmission, but then you should not buy a rust bucket trans to begin with.
Those detent springs are common to many different transmissions. Those springs are not made by GM rather by a supplier. Same springs are used by GM, Ford, Dodge and many others. Find similar three speeds of the same vintage years, buy detent springs when you find those, if a cheap price. Upon arrival, toss your springs into small plastic bag, write up a label, "1956 Ford", shove this in your bag with springs, then store away. Next set, "1951 Jeep Saginaw", store away. Next, "1947 Fleetmaster", store away. Collect yourself several sets, dozens of sets if cheap. Amongst those you will have the right set of springs or close enough. You can later sell on Ebay what you do not need, or simply keep them for the future.
Detent springs only need to be 'about' the right length and 'about' the right diameter. A little too long, a little too stiff is better, never use too short of springs nor too soft. Those detent springs only control how 'firmly' a gear is held in place, not much else. Those springs only work right when your trans is in good repair. Those springs will not overcome major problems. Think of those springs as a "courtesy" for drivers, something to sorta keep your trans in gear. Purpose is solely to keep gears from gently "drifting" out of alignment, like when you are coasting along downhill, keeps gravity from moving your gears around.
Don't sweat the small details, find some springs very similar, stiffer the better, and go with those. You might be surprised to find some generic springs which will work at a cheesy Autozone store.
On your shift forks, you write:
"A core is needed - they must have these rebuilt."
Yes, rebuilt at a machine shop. Price is about $60 on your web page. This is a good price, probably less than what a machine shop would charge you to rebuild yours. When a 'core' is needed to exchange, your new part will always be rebuilt. This is OK.
You ask,
"Is the reverse-first fork not usually a problem?"
Correct. Key term is "usually". Those gears are used less than second and third. Reverse is used the least. Wear is spread out over four tabs, less wear per tab. Nonetheless, replace or rebuild the fork anyhow.
When you go through the trouble of dropping out a trans, or pulling an engine, go ahead with a full rebuild, do this right. If not, you will regret this later when something else fails.
Gears almost never need to be replaced. This only needed when a tooth is severely broken or other major damage. A little bit of rounding on teeth corners, no big deal; shifts smoother.
Sliding parts, like a sliding clutch gear or a sliding second gear, take a look at where the shift forks engage. Shined up from use, just fine. Should there be a 'ridge' then this is a problem.
Bearings and seals, those are to always be replaced no matter how good those look. You cannot precisely measure to determine if bearings are out of tolerance. Only a few thousandths out of tolerance causes a noisy transmission. Most often, you can pull a part number off the side of a bearing, like a Timken number. Same is true for seals. Easy enough to look up a catalog bearing or seal part number with disregard to what year and model of car. Bearing, seal and gasket kits are all over the web.
There is a boy on Ebay who sells complete gears sets, synchros, bearings, seals and gaskets, I mean the complete works, everything inside a transmission. A bit pricey, $200 to $400 but you will have virtually a brand new transmission good for fifty years or more.
Don't be afraid to rebuild a transmission. Those are so darn easy. Just get yourself a shop manual, or copy of instructions from a shop manual, a cakewalk. Old 'Motor Manual' books are available on Ebay, $10 to $30 on the average. Only need to be careful what years are covered. I have a collection covering about 1936 through about 1970, both car and truck versions. If you need a copy of instructions, just ask. Obviously I have a Motor Manual covering your transmission. You will be more pleased to have a manual of your own; loads of info about all aspects of your truck.
Don't be afraid, just use a bigger hammer.
Billyray
