A popular scenario is Reagan nominating Bork for Rehnquist's seat in 1986 and Scalia for Powell's seat in 1987. This probably would have worked as the Republicans controled the Senate in 1986 and there would be less opposition to Bork succeeding Rehnquist, the most conservative Justice, than succeeding Powell, a moderate conservative and a swing vote. Scalia hadn't yet said anything as controversial as some things Bork had said and had the advantage of being an Italian-American. However, unlike others, I don't think this necessarily means a more conservative Supreme Court. In 1991, more Senators may have thought the Supreme Court was too conservative and voted against confirming Clarence Thomas.
Thinking about this, it makes sense why they didn't go for Bork in 1986. Scalia was a bit less conservative on racial discrimination issues than Rehnquist or Bork (the latter two argued for the right of private people [not government] to discriminate, whereas Scalia had done no such thing). To put up *two* nominees in 1986 who cast skepticism on the Constitutionality of part of the Civil Rights Act of 1964 would have been thermonuclear.
If the goal is to get Scalia and Bork on the court, it would make more sense to leave Rehnquist as an Associate Justice and just nominate Bork to be Chief Justice. Bork's 42-58 defeat in 1987 OTL might go go differently without the preparation the Democrats had done in anticipation of his nomination and there being 8 additional Republican Senators.
Scalia would proceed to get confirmed in 1987 because he'd be an easier sell than Bork for the reasons mentioned already (less inflammatory civil rights positions, less of a paper trail, Italian-American, etc.).
In his later years, Rehnquist's efficacy on the court waned. As he got older, he didn't have time to do the duties of Chief Justice and act as a Conservative crusader on the bench. He'd probably be much more Conservative and focused on that.
Bork being confirmed could either hasten Thomas's advancement or prevent it entirely. Thomas was put on the DC Circuit in 1990 following Bork's retirement. If the seat opens up in 1986 instead of 1990, it could either mean Thomas is put on the bench 4 years earlier OR that there is no opening for Thomas in 1990.
Without the memory of the 1987 Bork fight, Republicans won't be as intent on going for a 'stealth candidate' in 1990 or 1991.
The HW Bush Administration viewed Edith Jones and Lawrence Silberman as too openly Conservative following what a mess the Bork and Ginsburg nomination attempts had been, and without their nomination it is unclear if the same strategy would be pursued that lead to Souter being picked as stealth candidate. HW could end up nominating one of several conservative names to replace Brennan - Edith Jones, Laurence Silberman, Douglas H Ginsburg, or Clarence Thomas (4 years on the bench here). Or it could be a moderate to centrist pick like Anthony Kennedy, Ken Starr, or David Souter. Kennedy and probably Starr would both be more Conservative than Souter though.
If Thomas isn't an option in 1991 to replace Marshall, then the options are Emilio Garza (who'd only been on the Court of Appeals Bench a couple of months) and ... not a lot of other Conservative picks who aren't white guys. Maybe Jose Cabranes, under the idea that a centrist would still move the court in a preferred direction. Or they could go with Edith Jones. Abraham David Sofaer is another prospect - an Indian-born Jewish-American, a District Court Judge in the prestigious Southern District of New York, ally of Daniel Patrick Moynihan previously, and a Republican since 1984.