I have the same trans as yours. a 235 and a 390 posi. I don't go over 60-65 and when I start out I start in 2nd gear with no issue.
It works great.


1961 Long Stepside Apache 10, original 235, 4 speed and 3:90 posi totally stock (owned 12 years)
1966 Chevelle (owned 53 years)