i to like when the FEL is for most part fully raised. it allows me to get into certain parts that i would other wise not be able to get into.
majority of tractors i have seen. normally always have a U shape like piece of metal, that hinges on one side. and then goes around the cylinder. and when you lower the FEL some. the weight of the FEL and bucket. basically holds everything together. and keeps the FEL from dropping.
though on another note. I HATE GETTING UNDER IT! all it is, is that one piece of metal. and if you have to hammer something. or pry something. and hit that one support hard enough by accident you could be in, a lot of deadly trouble real quick! thankfully all my hydraulics are all tight and good. exception boom cylinder on backhoe. after a 24 to 48 hour period it is fully collapsed

but i still can't rely on hyd pressure still built up in the cylinders as a backup. to easy to hit a lever, and let things drop in a heartbeat.
so i generally rely on having a second person around. i really don't care who it is. as long as they actually stay around. and keep an eye on me. if they don't have eye contact with my body, i can get rather agitated rather quickly. and normally give that person a heads up of, going to be doing something dangerous that could... yada yada. so pay attention. and then when done let them know. so they can click on computer / text / or what not. but still be near by.
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as far as "reading owners manual) FEL (front end loaders) it could be original manufacture type (same as tractor) or it could be third party FEL. i have seen a lot of mix and matching on older tractors.
best bet, is hit the manufacturers website first and see if they have owners manuals listed. most likely if they do. they should also have a FEL listed if tractor had option to come with one. if not same FEL, there should be some sort of "stamped" in numbers (model / serial) some place on arms. that you could look up.
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i am hesitant to say use a 2x4 or something and prop the FEL from the ground. it can be rather easy at times to shift the tractor around enough. to cause a single 2x4 to slip off. even if you have the wheels of tractors blocked so the tractor can not roll on you.
perhaps as a backup option. get a ball valve that can handle the max pressure of your tractor 2000 or 3000psi (others be able to say better) and put them in line with your lines going to the FEL. so you can close the ball valves. and make sure you can hold the pressure in the cylinders to keep the FEL up. ((don't buy them generic brass gas valves at local hardware stores they are not rated at high enough pressure)) they would need to be much more costlier valves.
as far as a brace. i would see about custom making something. that i could use some pins to physical hold a piece of metal in place. and attach to arms and then attach to the sub frame of the FEL or sub frame of tractor. so only way FEL could drop is by physically removing the pins and then the piece of metal. (piece of metal being anything, bar channel iron, pipe, what ever, as long as it is strong enough metal and you can securely get the pins in. ) i suppose a U channel, Square channel, L channel would more likely be better options for this. i suppose a metal pipe could be used.