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Can my 51 AD's transmission be removed without stripping the nose and pulling the engine with it?

What size truck?
What transmission?
Do you have the original torque-tube (enclosed drive-shaft)?
Do you have a Shop Manual (see link below)?

http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0704.htm

On a 1/2 ton:

Both the 3-speed and the 4-speed transmission on a 1951 truck can be removed by:
- disconnecting and moving backwards the u-joint cover,
- disconnecting the u-joint,
- raising the drive-shaft,
- unbolting the transmission,
- pulling the transmission rearward, and then
- removing the transmission downwards (the Shop Manual says to remove it upwards through the hole in the floor)

Maybe someone else will comment on the transmission rear mount and if the rear-mount cross brace/bar can be removed.

Make two "guide shafts" by cutting the heads off of 4" or 5" bolts the same diameter as the transmission attachment bolts. Swap the bolts with the top two transmission attachment bolts.

Note: the two lower transmission attachment bolts have their heads inside the clutch housing (remove the clutch housing bottom sheet-metal cover to reach these bolts).

it's a 51 short bed with a 4 speed I thank you very much for the information. I didn't really want to have to strip it all down!

The one thing I do not know for sure is can you remove the frame cross-brace at the rear of the transmission (is the a rear mount on the transmission)?

Removing and re-installing the 3 speed transmission is much easier if you remove the cross member at the rear of the transmission. There are about 12 bolts holding this cross member to the sides of the frame. This is the cross member that the rear transmission support mounts to. In fact, I could not figure out how to re-install the rear transmission support with the cross member in place. Also, as Tim suggests be sure to use the guide supports at the top of the transmission when pulling the transmission. If you don't it's easy to either damage the springs on the pressure plate or cause the clutch to become mis-aligned. I just went through this a couple of months ago and you almost need a second set of hands to wiggle and turn the throw-out bearing onto the snout of the transmission and you are guiding the transmission into position.
Mike

It really helps on reinstallation to have an alignment shaft to get everything lined up. I use an actual shaft from a discarded transmission, but I think Summit Racing sells plastic versions.

Try and use an actual shaft, the plastic ones in my book just don't cut it.

Thanks, Mike

Note to inexperienced readers: is is quite common to come across a pre-1954 truck with no rear-transmission cross-member. They were often removed and never put back on after a transmission removal/installation. This puts excessive strain on the rear engine mount.

The 1954 trucks with manual transmissions have no rear transmission mount. The 1954 Hydra-Matic has a bolt-on transmission-mount cross-member (and a bolt-on rear-engine/front-transmission cross-member).

I'm with Brian: if you have an old transmission front-shaft, use it. However, the plastic alignment tool is far better than using no tool. Using no tool is close to an exercise in futility.

Assembly: Step 4
2. K-411 (I have never seen one, except in Shop Manuals)