If it worked fine before, there is prolly nothing wrong with it now. Sometimes, without the engine running, it can be really hard to get the trans to engage a particular gear. Have you tried rolling the car a little forward/backwards to see if the trans would shift? Without the input shaft turning, the splines of the synchro teeth may just be in a position to block the shift....moving the car would allow them to align, and allow the shift to take place. It would also eliminate any "bind" that the trans may be in from sitting.
Other than that, I can't think of anything that would keep you from being able to manually manipulate the shift levers on the side of the trans, and shift into 3rd/4th.
http://s77.photobucket.com/albums/j54/aapple2/Misc%20pics/350%20Trans/4speed%20stuff/?action=view¤t=side.jpg
|UPDATED|10/5/2012 9:52:39 AM (AZT)|/UPDATED|
______________
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"