New to Mopar

69 could indeed be a 273, but check the casting numbers on your block. Pistons in those years are almost zero deck, so compression will be fine. 1.88 intake valves fit without notches, but check valve clearance to bores without the pistons. You can mill the 587's to get to 65 cc, then 300 hp is pretty easy. Plus you won't have to rebuild it as much as a 327.