Here is a bigger picture of the first letter, and I have come across a second letter as well:
One thing that we can examine is the signature, if it is an exact duplicate, that would show that it was just fabricated on this picture.
Another thing we can examine is that there are other versions of the letter in English floating around. Some people say that the originals are in Punjabi and that these are English translations. One person online translated it like this:
________________________________________
(Confidential /secret)
April 25, 1984
Mr. R.K. Dhawan
1, Safdarjang Road
New Delhi.
Dear Dhawan Sahib,
As you may know that there is a danger to the life of Sardar Gurbachan Singh, so I am writing this letter to you. (To now) Sant Jarnail Singh is sticking to his views. I feel that now we have to do that which we have already planned for and that which Parkash Singh Badal has already explained to you in detail. Bhinderanwale’s men would run away seeing the army and very likely he too would also run away.
Maj. Gen Jaswant Singh Bhullar and Prof. Manjit Singh (Sidhu) have agreed to go to America. They have been given complete instructions, and they would also meet with you before going to America. The arrangement for their expanses has been made. An American resident Didar Singh Bains and Jagjit Singh Chauhan will work with them. They have been instructed that they organize the Sikhs living in foreign countries before hand, so to prevent the Sikhs from organizing themselves in favour of Bhindrawala..
Please, ask all your men to help them (Maj.Gen Jaswant Singh Bhullar and Prof. Manjit Singh Sidhu) in every possible way.
Very shortly (soon), we shall provide you the names and addresses of those Sikhs who are helping Sant Jarnail Singh. I am very hopeful that our plan will be succeed and we shall soon be free from this curse.
Yours Well-wisher,
Sant Harchand Singh Longowal.
_______________________________
^ From above we can clearly tell that in the Punjabi version, the ending is not written as "Yours very sincerily" and it is probably "(Tuhada) Shubh Chintak" (as commonly written at the end of Punjabi letters).
Also, it was published in some 'Sikh Weekly' Journal, which is supposedly created by Kala-Afghana/Darshan Ragi group. The journal/website doesn't even exist anymore I think.
"The Sikh Weekly of June 4, 2010 has published a confidential letter written by Harchand Singh Longowal to Indian Government (Mrs. Indira Ghandi’s office) about a month before the Operation Blue Star took place. In the letter Longowal is asking Mrs. Gandhi to execute the plan. The letter is published on page 13 of The Sikhweekly .It is in the right hand side column at about the bottom of the page."
Here is more information:
"LETTERS FROM HARCHAND SINGH LONGOWAL
According to Dr. Gurmit Singh Aulakh, President of the US based Council of Khalistan the
seven letters written by Harchand Singh Longowal and his secretary Gurcharan Singh are conclusive evidence that the entire Akali leadership has betrayed the Sikh Nation. Dr Aulakh opined that the Akalis connived with the Indian government in 1984 and they have been betraying the Sikh Nation ever since.
(One wonders, where are original letters for verification of 'Signatures')
Harchand Singh Longowal was so cunning that he was successful in sidelining the politicians like Parkash Singh Badal and Gurcharan Singh Tohra after Operation Blue Star, and he was the man behind Surjit Singh Barnala. Akali Dal is of the opinion that there is no doubt on the fact that Longowal, Tohra and Badal were having strong ties with Delhi masters and even intelligence officials, but Akali Dal in any circumstance, can't digest the following letters, as if they were written(that too typed one) by the cunning mass-ranger like Longowal and Gurcharan Singh, who were successful in befouling Sikh Quam and even Badal & Tohra. Lastly, person who works for secret agencies never write like this."
[
ssosan.tripod.com]
Now where are the other 5 English translation versions?
Also where are the 7 Punjabi original versions?
I don't think these allegations are that small that we can just say "they're fake" and look away.
This is something which really needs to be investigated.