Instead of "license=('GPL-3 | file LICENSE')" use "license=('GPL3' 'custom')" if there are other custom licenses involved. "license" in the PKGBUILD is an array so each license has to be specified separately.
Also consider adopting the r-cran-* packages or ask the maitainers to convert them to r-$modulename since it will be consistant with what was discussed earlier.
-- Regards Jagan
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