The data sheet says that it should be the HXB2 sequence:

"...

Description:

An HXB2 proviral fragment from nt 5496 (an artificial SalI site) to the 3'-terminal LTR was inserted into the SP64 polylinker SalI-XbaI site. The 3' HIV-1 LTR and SP64 polylinker were inserted in place of the SV40 early promoter and the dhfr gene from SV2-dhfr. The Tat-responsive HIV-1 LTR is used to promote expression of HXB2 rev and env.

..."

HXB2 env gene starts at base 6225 in the HXB2 genome:

https://www.hiv.lanl.gov/content/sequence/genome_browser/browser.html

And the papers by Dr. Sodroski discussing the plasmid states that they started with the HXB2 genomic clone.  See attached PDFs of the papers.

https://www.aidsreagent.org/reagentdetail.cfm?t=expression_vectors&id=145

Plasmid_pIII_Published.pdf

Thanks both.

I finally managed to sequence it, I guess that something went wrong the first time.

Best!

Please let us know if you find a difference from HXB2 sequence.  I am glad you got the sequenceing working for you.