55.2-59 Help identifying driveline parts please?

[County]

Father in Law has a '55 series 2 GMC 4x4. Was all original when he got it as far as we know. The original engine was not rebuild-able, but was a 288(maybe?) v8.

So, new rebuild motor he was told is a 400sb. Can someone verify from casting? casting numbers on rear of motor, not on pad on front of head.



Please identify trans as well? 3sp or 4 sp? Seems to be only 4 gates, so thinking 3 fwd and reverse, but very jammed up and tough to move unsecured.

Old Muncie M20 maybe?







Thanks for the help identifying what we have!

-Shayne