Nope. 481988 is a 1971-1975 400 casting. Look again at the casting date and engine code. There are no XR code 481988 in my reference materials. XR were 326, 350 and 301, and there should be one or two more numerals in the engine unit number.
You have a date that doesn't coordinate with the casting, and a stamped code that does not coordinate with displacement and casting.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
