5: 1975 model year
225: Duh
2 8 7: proof Chrysler were in such shambles in 1975 they could lose toilet paper on its way from the roll to their backside. Instead of the 4-digit number referring to the 10,000-day calendar that "should" be there, roughly from 4767 (16 Aug '74) through 5110 (25 July '75), that's an olde-tyme date stamp suggesting the engine was built on 8 February 1975, with the "7" meaning a production line, a shift, or the stamper's favourite number.