How to produce a margintable (in a LaTeX tufte-book) using kable or xtable or a combination - knitr

Question

In an Rnw document with
\documentclass[twoside,nobib,ls,notoc,nofonts]{tufte-book}
<<>>=
library(tidyverse)
library(xtable)
library(kableExtra)
#
which is to be compiled with knitr followed by pdflatex.
I have a tibble:
tb <- tibble(measure = c("mean", "variance"), mean = c(24.4, 0.808), median = c(24.5, 4.37), efficiency = c(NA, 0.185))
I'm trying to produce a margintable:
\begin{margintable}
\caption[Results]{\label{tab:bootstrapEfficiency}Results of bootstrap}
\centering
\begin{tabular}[t]{lrrr}
\toprule
\multicolumn{1}{c}{} & \multicolumn{2}{c}{measure of location} & \multicolumn{1}{c}{} \\
\cmidrule(l{3pt}r{3pt}){2-3}
\rotatebox{45}{measure} & \rotatebox{45}{mean} & \rotatebox{45}{median} & \rotatebox{45}{efficiency}\\
\midrule
mean & 24.4 & 24.5 & NA\\
variance & 0.8 & 4.4 & 0.18\\
\bottomrule
\end{tabular}
\end{margintable}
kable doesn't produce what I hoped it would:
kable(bootTb,
format = "latex",
booktabs = TRUE,
caption = "Results of bootstrap",
caption.short = "Results",
label = "bootstrapEfficiency",
digits = c(0, 1, 1, 2)) %>%
add_header_above(c("", "measure of location" = 2, "")) %>%
kable_styling(full_width = FALSE, latex_table_env = "margintable") %>%
row_spec(0, angle = 45)
The output is:
\begin{table}
\caption[Results]{\label{tab:bootstrapEfficiency}Results of bootstrap}
\centering
\begin{margintable}{lrrr}
\toprule
\multicolumn{1}{c}{} & \multicolumn{2}{c}{measure of location} & \multicolumn{1}{c}{} \\
\cmidrule(l{3pt}r{3pt}){2-3}
\rotatebox{45}{measure} & \rotatebox{45}{mean} & \rotatebox{45}{median} & \rotatebox{45}{efficiency}\\
\midrule
mean & 24.4 & 24.5 & NA\\
variance & 0.8 & 4.4 & 0.18\\
\bottomrule
\end{margintable}
\end{table}
Which is not correct LaTeX. Of course removing latex_table_env = "margintable" produces a fine LaTeX result, but one that can't be wrapped in a margintable.
In contrast,
xtable(tb) %>%
print.xtable(type = "latex",
floating = FALSE,
booktabs = TRUE,
rotate.colnames = TRUE)
produces
\begin{tabular}{rlrrr}
\toprule
& \begin{sideways} measure \end{sideways} & \begin{sideways} mean \end{sideways} & \begin{sideways} median \end{sideways} & \begin{sideways} efficiency \end{sideways} \\
\midrule
1 & mean & 24.40 & 24.50 & \\
2 & variance & 0.81 & 4.37 & 0.18 \\
\bottomrule
\end{tabular}
which can be placed in a ```margintable`` environment, but the column names are not rotated 45 degrees, and there's no additional header above them.
I tried to use xtable2kable but couldn't see how to get it to produce the desired result.