Shifter Problems...

Hello all, I just picked up a ‘71 demon. It was originally a slant 6 / column auto car, but one of the previous owners swapped a 360 and a four speed into it. After I got it home and off the trailer, I test drove it up and down my street but was unable to shift into 2nd gear, because when I let off the clutch, the trans started grinding so I limped back home in 1st. It has an odd shifter, nothing I’ve ever seen in a Chrysler, which made me question whether it’s even an 833. (I am yet to put the car in the air and look.) It has a reverse lockout on it and you must pull down on the shifter instead of up to engage reverse. Do any of you think changing out the shifter would help? If not, I’m wondering if there’s slop in the linkage and it needs to be adjusted, or if it’s a syncro issue. What are your thoughts? Thanks for reading.