Although the Jatayu fight gives evidence both ways (both 10+ arms and 2 arms)
The final combat with Rama seems to show Ravana with only one head and two arms: this has to be more weighty evidence - since if there was ever a need to use his 20 arms - this was the time.
ततः क्रोधान्महाबाहू रघूणां कीर्तिवर्धनः |
संधाय धनुषा रामः शरमाशीविषोपमम् ||६-१०७-५४
रावणस्य शोरोऽच्छिन्दच्छ्रीमज्ज्वलितकुण्डलम् |
तच्छिरः पतितं भूमौ दृष्टं लोकैस्त्रिभिस्तदा ||६-१०७-५५
54-55. tataH = thereupon; raamaH = Rama; mahaabaahuH = the great-armed; kiirtivardhanaH = and who augmented the fame; raaghuuNaam = of the kings born in Raghu dynasty; krodhaat = with anger; samdhaaya = stretching; aashiiviShopamam = the serpent-like; sharam = arrow; dhanuShaa = with his bow; achchhindat = chopped off; raavaNasya = shiraH = the head of Ravana; jvalita kuN^Dalam = which was graced with blazing ear-rings; tadaa = then; tat = that; shriimat = glorious; shiraH = head; dR^iShTam = was seen; patitam = fallen; bhuumau = on the ground; tribhiH lokaiH = by the three worlds.
Thereupon, the great-armed Rama who augmented the fame of the kings born in Raghu dynasty, stretching with anger, the serpent-like arrow with his bow, chopped off the glorious head of Ravana, which was graced with blazing ear-rings. Then, all the three worlds saw that head, fallen on the ground.
तदप्यशनिसंकाशैश्छिन्नं रामस्य सायकैः |
एवमेव शतं चिन्नं शिरसां तुल्यवर्चसाम् ||६-१०७-५८
- tadapi = that head too; chhinnam = was chopped off; raama saayakaiH = by Rama's arrows; ashanisamkaashaiH = which were looking like thunder-bolt; evemeva = in the same way; shatam = a hundred; shirasaam = of heads; tulyavarchasaam = of equal splendour; chhinnam = were chopped off.
Rama chopped off that head too with his arrows looking like thunderbolts. In the same manner, a hundred of Ravana's heads of equal splendour were chopped off by Rama.
Vibhishana's grief over Ravana's death:
निक्षिप्य दीर्घौ निश्चेष्टौ भुजावङ्गदभूषितौ |
मुकुटेनापवृत्तेन भास्कराकारवर्चसा || ६-१०९-३
3. dirghau bhuhau nikShipya = having thrown about your two long arms; aN^gada bhuuShitau = which though decked with armlets; nishcheShTau = are (now) motionless; mukuTena = and with your diadem; bhaaskaakaara varchasaa = brilliant as the sun; apavR^ittena = knocked down; (why are you lying killed on the ground?)
"Having thrown about your two long arms which though decked wit armlets, are now motionless and with your diadem brilliant as the sun, knocked down; why are you lying killed on the ground/"