Should David Ortiz Play First Base In the World Series?

I have the mixed blessing of living in New England, so I unavoidably run into local sports radio once in a while. They’re already looking ahead to the Red Sox’ inevitable World Series appearance, and of course given David Ortiz’s unprecedented combination of offensive skills and just incredible foot pain/immobility, there’s a legitimate question of whether the Red Sox should play him in the field when they lose the DH in World Series road games. Just a quick-hit here on some of the relevant numbers.

I’m not going to address in this article the extent to which playing the field might limit his ability to hit or run. I don’t dispute that that could be significant, but I have no idea how to value that.

The way I see it, there are three options:

1. Move Hanley Ramirez over to 3B, play Ortiz at 1B, take Travis Shaw out of the lineup.
2. Replace Ramirez with Ortiz at 1B, keep Shaw.
3. Don’t start Ortiz, but do pinch-hit with him in a high-leverage situation.

We’ll make the following assumptions: I’m going to estimate that Ramirez will have the same defensive value at 3B that he had last year in LF (-22.9 runs), and I’m going to further estimate that Ortiz will have the defensive rating of some of the worst 1Bs in baseball over the past few seasons (-25 runs). Travis Shaw was worth 6.6 runs of defense playing mostly 3B this year. Ortiz was worth 27.6 runs of offense + baserunning, Ramirez 17.1, and Shaw -10.3. We’ll estimate that playing Ortiz would get him 4.4 plate appearances per start, whereas if he doesn’t start, he gets one plate appearance in a situation that has a leverage index of 2.

Scenario 1: Ortiz gives you 2.6 runs at 1B, Ramirez -5.8 runs at 3B, total of -3.2 runs.
Scenario 2: Ortiz gives you 2.6 runs at 1B, Shaw -3.7 runs at 3B, total of -1.1 runs.
Scenario 3: Ramirez gives you 1.8 runs at 1B, Shaw -3.7 runs at 3B, and Ortiz gives you 27.6*(1/4.4)*2 = 12.5 runs at PH, total of 10.6 runs.

Seems like the best option here by a decently wide margin is to use him as a pinch-hitter, and I’m surprised at how much of the value comes from just the pinch-hit appearance. Fairly robust to my assumptions, too — if you assume a leverage index of 1 in his one plate appearance, you still get the highest total with Ortiz as a PH. You could also give him a defensive rating of -15 (which would be incredibly generous) and the PH scenario comes out on top. Anything else I’m missing? Other lineup options for the Red Sox?