Here is a history of the vote from 1986. It initially passed the Senate in 1985, with 69 votes, but didn't pass the House until a year later, and the conference report only passed with 63 votes. BUT the point is they worked on the bill for over a year after introduction, and we don't have no year to work with, only a few months.

DAUser, it seems they had a lot more support in Congress. Popular support was a very different thing just because the ethnic makeup of the country was different, and so was the immigration system.