  We present results from an optical study of two young Balmer-dominated
remnants of SNIa in the Large Magellanic Cloud, 0509$-$67.5 and 0519$-$69.0, in
an attempt to search for signatures of efficient cosmic-ray (CR) acceleration.
We combine proper motion measurements from HST with corresponding optical
spectroscopic measurements of the H$\alpha$ line at multiple rim positions from
VLT/FORS2 and SALT/RSS and compare our results to published Balmer shock
models. Analysis of the optical spectra result in broad H$\alpha$ widths in the
range of 1800-4000 km s$^{-1}$ for twelve separate Balmer-dominated filaments
that show no evidence for forbidden line emission, the corresponding shock
speeds from proper motion measurements span a range of 1700-8500 km s$^{-1}$.
Our measured values of shock speeds and broad H$\alpha$ widths in 0509$-$67.5
and 0519$-$69.0 are fit well with a Balmer shock model that does not include
effects of efficient CR acceleration. We determine an upper limit of 7%/$\chi$
(95% confidence) on the CR acceleration efficiency for our ensemble of data
points, where $\chi$ is the ionization fraction of the pre-shock gas. The upper
limits on the individual remnants are 6%/$\chi$ (0509$-$67.5) and 11%/$\chi$
(0519$-$69.0). These upper limits are below the integrated CR acceleration
efficiency in the Tycho supernova remnant, where the shocks predominantly show
little H$\alpha$ emission, indicating that Balmer-dominated shocks are not
efficient CR accelerators.
