They should be the same pretty close. Is the 68 stock? I don't remember the 68 289 being available with 4bbl. The 2 bbl 289 was only one listed and it had 10 less HP. This was a transition year from the 289 to the 302 and I have heard that there are some with mixed 289/302 parts and even rumors of a couple 302s badged as 289s.

 

There was no 289 4 bbl offered in 1968. There was a 302 4 bbl in 1968 (engine was available for 1 year only). There was a 289 2 bbl in 1968. My level of knowledge mostly relates to the 1967-1968 model years. As I recall, the compression ratio was slightly higher in the 4 bbl engines through the years, requiring the use of premium fuel. As far as intake manifolds, they would interchange. Carburetors would be Autolite models, be it the 2100, 4100 or 4300. So in a nutshell, very similar but slightly different. Hope that helps.

 

quite right. compression ratios however were varied. the rated compression ratio for two barrel 289s was 9.5:1 iirc, and four barrel 289s and the 68 302 was 10:1, again iirc. however that assumed that the dished pistons were in fact installed in the two barrel engines while the flattops were installed in the four barrel engines. back in the day it was not uncommon for either piston to be installed in either engine. my c code 289 for instance had flattops installed from the factory, and i have seen dished pistons installed in four barrel engines, specifically a code engines. as far as i know all k code engines got the flattop pistons. as for the 4300 carb, i thought they came along in the early 70s on the 351c 4v engines, and the 429 4v engines.

 

As said, only a 302 4v in 68. '66 289 heads and '68 4V heads are very similar. So biggest difference is the intake and carb and the 13 cubes.

 

How could I tell if it's a 302 in the '68? Here's a pic. I wish I had a pic of the label on top of the air filter!

 

assuming the engine is untouched, if it has the four barrel carb, its the 302. if it has the J engine code, its the 302. otherwise it is the 289 c code two barrel engine.

 

There were several small block V8 engines offered by Ford in 64 1/2 thru 68 Mustangs. F, D, C, A, J and K.

o F was 260 cu.in. early 65 (64 1/2) 2V. Regular fuel.
o D was 289 cu.in. early 65 (64 1/2) 4V. Regular fuel.
o C was 289 cu in. 65 thru 68 2V Regular fuel.
o A was 289 cu.in. 65 thru 67 4V Premium fuel
o K was 289 cu.in. 65 thru 67 4V Premium fuel high performance
o J was 302 cu.in. 68 replaced the A. 4V. 1 year only.