the stamp near #1 cyl is the engine buid completion date. its usually a date code folled by a shift number, ot similar after.
mine is 7L13 A if I recall correctly.
if you dont have the flat section as shown previously, you may have an actual 289 block. in 68 they used them all up and any extra 289's have 302 blocks. I have seen feb C codes with both 289 and 302 blocks.
if the stamp is near the back, it could be a partial vin from tge Kansas plant in 68 off a maverick, with a few numbers missing of badly stamped... 8k13 would be well into the 69 production year making a 289 block very unlikely. but if its 8k as a partial vin, tge engine could be anywhere from mid 67 to early 68.
have look for tge engine build date. it should help in this instance. beside of slightly under tge head at cylinder 1.