Technical chevy 307 or 327???

Hi.
looking at picking up a 68 c10 with a "327". In researching the casting numbers it shows that it could be a 307 or 327. On some sites it states that it could even be a 350. Is there any way to definitively tell the difference without tearing it open? the numbers on the block are GM13, 3914678, f248. The numbers on the heads are f218, 3911032.
New to joining here and want to thank everyone for their posts that helped me resurrect a 216 in one of my 50 3100s. This is a cool resource.

 

is there a number stamped on the front of the block? p*** side, just in front of the head, on the deck surface.

edit: I looked at a more specific list of casting numbers, which shows that that block was a 4" bore, and that means it would be a 327 (same casting was also used on the 302 and 350 in 1968) But it would be a good idea to look for the stamped numbers, to verify

 

Thanks for the help, unfortunately there are no numbers stamped in that location. The guy did a lot of performance upgrades which would lead me to believe it us not a 307, yet I've had guys try to sell me a 216 saying its a 292 (just a bit easier to discern).

 

The only way you'll know is to measure the stroke, or at least look at the shape of the crankshaft flange at the back of the engine. 302 would be round, 327 has two notches, 350 has two notches and a lip on the opposite side, as i recall, but you better look it up.

(I'm just hinting that if he had the block decked, he could have changed the stroke too)

 

It'll be a 4 inch bore large journal block. Odds are it started life as a 327 and still is unless someone wanted to change cranks and make a 350 out of it which is pretty unlikely. The heads indicate that it was a lower horsepower 2 bbl motor. Of all the small block chevys the 68 and 69 large journal 327 would be one of my favorites.

Also, the 350's had larger harmonic balancers than the 327 but it could have either on it by now,

 

Most 307 have casting number end with 0020. 40 to 45 years ago when 350 were impossible to get at a reasonable price a local Huntsville Alabama machine shop [Howards}} would buy junk yard 307 bore to 4 inch and build what you wanted302 327 or 350.. Most were 350 for circle track use.

 

Does it have the original draft tube hole?

 

68 probably would be a big bearing block with no draft tube, eh?

 

If its a 350, wouldnt it have the 5/8" spark plugs. I believe that started in 69 though.

 

The small spark plugs started in 1970.