MM, yep! ugly truck. Yep! rusty trans!
That looks like early 4spd to me with straight cut gears will be non-synchro. I was thinking that a later (48 or newer) SM420 was about same and can be had with enclosed driveshaft if you look in 1/2 tons with 4spds till guy above says have diff bolt pattern on b/house. Looks about same, must not be much diff. One thing strange, it has a taller shift tower maybe for shorter throw as longer lever and guys stood many times driving these delivery trucks. I think the B 27 9 mark is a date code. B=February 27=day 9=39? And the other # 590414 or 474 is the trans part #. Now to find someone with old parts book!
It would be worth it to change bellhouse and newer trans to get synchros. Open drive would need whole rear end changed. Have to remove clutch and flywheel to get housing off, bolts are behind the flywheel, great huh? Good Luck!
