Remove the starter and you'll find a pad on the oil pan rail edge that has the casting numbers... 1st digit c=60's d=70's e=80's f=90's, 2nd digit is the year, 3rd is model type (rather general for passenger cars, T=truck), 4th is the part type E being engine... the 5th, 6th, 7th, and 8th is the part descriptor (6015=block, 6049=head and so on), the 9th digit is the revision number. Here's an example... D9AE-6015-A means 1979 passenger car engine block 1st revision.
You'll find numbers similar to these all over the engine parts. In the lifter valley of the block you'll find in addition to this number, a 3 digit code which is the actual casting date: day, month, and year.
So you know, there are differences in the internals between the "302's" and "5.0's". From '68 to late '77 the 302 engine used a 28oz. offset balance, '78 thru '81 early '82 non H.O. engines used a 35oz. offset balance. From mid '82 thru '94, the 5.0's had a 50oz. offset balance shared with the big brother 351W/5.8L engines. All 5.0L H.O. designated engines in stock trim shared the same firing order as the 351W/5.8L . From '78 to '81 a lot of 5.0's installed in FOX chassis with rear sump pans, had the dipstick on the driver's side going into the oil pan, with '82 and up on the driver's side going into the block. Yours being in the front could easily be accomlished by changing to an earlier production timing cover for the front sump oil pan.