Fantastic investigation indeed. Keep it up please.Sibipura is Jatapura of Ramayana
In Ramayana, Sarg 42 of Kishkindha Kanda mentions places in the west.
....Further, you will find a sea (Arabian Sea) in which many sharks and crocodiles live in. Near that sea, you will find a forest where Ketakee, Tamaal, Kaarikel (coconut) trees grow. After that you will find Murachee and Jatapura cities. Next you go to Avanti (this Avantee is another Avantee), Anglepaa and Alakshitaa.
After this you will arrive at the mouth of River Indus (Sindhu). Near it is Hem Giri Parvat (Som Giri Parvat) which has numerous summits and on which there are many huge tall trees. Here live flying lions who take Timi named Matsya (fish or sharks) and elephant seals on the trees. You will search this mountain thoroughly.
Here we find mention of Jatapur city means 'the city of Jats' near Avanti and after it is situated Sindhu River.
वेलातल निवेष्टेषु पर्वतेषु वनेषु च ।
मुरची पत्तनम् चैव रम्यम् चैव जटा पुरम् ॥४-४२-१३॥
कपयो विहरिष्यन्ति नारिकेल वनेषु च ।
तत्र सीताम् च मार्गध्वम् निलयम् रावणस्य च ॥४-४२-१२॥
अवंतीम् अंगलेपाम् च तथा च अलक्षितम् वनम् ।
राष्ट्राणि च विशालानि पत्तनानि ततः ततः ॥४-४२-१४॥
सिंधु सागरयोः चैव संगमे तत्र पर्वतः ।
महान् हेम गिरिः नाम शत शृंगो महाद्रुमः ॥४-४२-१५॥
We can infer that Jatapura mentioned in Ramayana is same as ancient Sibipura and present Shorkot located in the Jhang district of Punjab, Pakistan.
The Sibi people when came to present Nagari near Chittor gave the name Jattaur which Al-biruni has written as Jittor. [The Jats:Their Origin, Antiquity and Migrations/An Historico-Somatometrical study bearing on the origin of the Jats, p.151]