Based on the 6-2-72 casting date, the first 3 in 3W360R3987
may be a "H" or a 'J'?
If so;
H - Series (model year) 1972
J - Series (model year) 1973
W - Windsor, Ontario engine assembly plant
360 - 360 CID
R - Regular fuel
3987 - 10,000 day date code for the final engine assembly - June 28, 1972
The VIN pad is on the passenger side of the block, down low, right above the oil pan rail. If it has no numbers on it, the engine may be an over the counter replacement or warranty engine.