the eleventh hour american proposal

Not exactly "eleventh hour", it was submitted on the 29th of Sept, 4 days after the Albanian (et al.) proposal on the 25th of Sept. A truely eleventh hour proposal can be seen with the Saudi Arabian A/L.638 submitted on the day of the vote (25 Oct.)

Also... From A/PV.1976:

Mr. MALILE (Albania):
[...]
73. The explanations we have heard here concerning draft resolution A/L.632 are completely unfounded. This draft is basically an integral part of the anti-Chinese attempt of the United States of America to legalize its "two Chinas" plot and is designed to sabotage the approval of the draft resolution of the 23 States, including Albania [referring to A/L.630, which would expel the RoC and invite the PRC. It became the draft that was adopted]. The content of such a draft is illegal. It seeks to open the way to the United States manoeuvre aimed at involving the United Nations in the domestic affairs of the Chinese people, which is the aim of draft resolution A/L.633 [keeping the RoC in the UN, but replacing it with PRC on Security Council]. As has been clearly pointed out, that draft resolution is in flagrant contradiction with Article 18 of the Charter. It goes without saying that the Article cannot be applied to our draft resolution.