Khan, 57, admitted that he initially put off reading Kulkarni's script, uncertain it would be possible to adapt such a "cult classic".
"It's like saying we are remaking 'Mughal-e-Azam' and 'Mother India'. It's not a wise thing to do," he said, referring to two Indian classics.
"But when I heard the script, I understood he's done it. It was a moving experience for me. I really loved it. The moment I heard it I wanted to do this."
Bollywood star Kareena Kapoor, 41, who plays Singh's lifelong friend Rupa, based on Robin Wright's Jenny Curran, said the plot was "timeless" with a love story at its core.
"I wondered how they would play around with such an iconic film," added Naga Chaitanya, a Telugu-language star from the southern film industry "Tollywood" who plays Bala, an adaptation of Gump's shrimp-fishing Vietnam comrade Bubba.
"But the way they have conceived the film for Indian cinema is unique."
Recent silver-screen hits have not come from Hindi-language Bollywood but are in other Indian languages, such as action flicks "Pushpa", "KGF: Chapter 2" and "RRR".
"RRR", released in March, raked in $87 million domestically, while "KGF: Chapter 2", which debuted a few weeks later, took in $106 million, media analyst Karan Taurani of Mumbai-based Elara Capital told AFP.
Action film "Shamshera", released on July 22 and starring Bollywood actor Ranbir Kapoor, has so far only made $5.6 million, dashing hopes it would lure audiences back to Hindi cinema.
A rare Bollywood hit this year has been comedy horror "Bhool Bhulaiyaa 2" released on May 20 and featuring rising star Kartik Aryan, which has brought in $24 million so far.
Now, all eyes are on "Laal Singh Chaddha" and family dramedy "Raksha Bandhan" with Bollywood megastar Akshay Kumar -- which also releases on Thursday.
Taurani estimates that "Laal Singh Chaddha" will make $19 million, falling short of Khan's per-film average of $35 million.
Khan, who co-produced "Laal Singh Chaddha", believes Bollywood hasn't lost its mojo, blaming the early release of movies on streaming services for lower box-office takings.
"I feel that perhaps we -- I'm including myself in this -- as Hindi filmmakers, need to... also pick topics which are relevant to a larger audience, as opposed to picking topics which are relevant to a smaller audience," he said.
