Before I twin sticked, I had difficulties shifting into and out of 4wd. I have a 76 with 302 C4 and J shift D20.
What I did to make it as easy as possible was to find a clear area, and put it in drive, while keeping some pressure on the t-case shifter, then shift to neutral, then shift to reverse. After doing this once or twice, it'd shift with no struggle. You just have to be patient and let things line up on their own.
Don't do like I did shortly after buying my Bronco, I got it into 4, and broke the stinkin shifter trying to get it out! It left me stranded, in neutral, and I didn't know what I had done. I had to get a tow back to the house, then I found out that I broke the 'finger' off of the bottom of the shifter. I had to buy another one for a few bucks from a local fella, and put that in. That was an embarassing lesson.
Save up your money, and do the twinstick upgrade. It'll make life so much easier.
Keep your rig clean, and stay out of the mud, and it'll work for a good long time to come.