Does McConnell have 51 votes to block witnesses in Senate trial?

I doubt it.

If he had the votes, he would be more vocal about wanting Pelosi to send over the Articles of Impeachment. Because Trump wants the vote taken immediately.

At this time, Trump seems to be working thru a couple of flunkies, Graham and Hawley, to try to force an acquital vote thru the Senate. Both are making absurd comments about changing the rules to permit a vote to dismiss the entire process with a simple majority vote.

Pelosi is getting ready, later this week, to vote on War Powers resolution, and will send it to the Senate for continued debate. She will be studying that vote very carefully, as it might relate to a vote for witnesses later.

At this time, McConnell and Pelosi are playing sort of a chess game with this witness issue. My hunch is that McConnell does not have 51 votes right now and is willing to drag it out until he has the votes or the pressure from the White House forces him to take a vote.

Meanwhile, Pelosi is collecting more and more evidence with each passing day to add to the evidence already there. There will not need to be more articles of impeachment, the House Managers will only add the new evidence to their arguments on the floor of the Senate.

Also, we now hear that Bolton has agreed to testify in the Senate trial if he is subpoenaed. This puts added pressure on McConnell and the Republicans.