B heads first appeared on an aluminum 4.6l block in a Lincoln Mark VIII. "B" represents the head model. Their was an "A" model that never made it to production and this model had a very distinct caracteristic and was 2 round intake ports. Ive only seen pictures of "A" heads and intakes, their for can not compare differences between A and B heads. However I can go into diffrences of B and common C heads(also uncommon C heads) Back on topic! B heads had a number of revisions that mostly consisted of improved manufacturing. Although their are distinct differences between lincoln B head and Cobra B head. Keep in mind by the time 1998 rolled around both makes carried the same head...or I should say carried very similar designed heads. You see....just because a head looks the same from either company doesnt necessarily mean they are the same. Such as npi heads from a 4.6l is in fact not the same npi head from a 5.4l. Same goes for pi heads. Heck I just recently discovered some npi heads were made in Mexico and have been in the process of disecting them. Subtle or big difference inside where the outside appearance can be very deceiving. Take for instance Lincoln B head valve guides. And Ive been preaching this for years! Folks will buy B heads to rebuild and have major issues with burning oil after 10k miles with no luck figuring out why! Ill preach about Lincoln valve guide seals are NOT the same as cobra untill mid year 97. The "guru's" would argue the point. They would also claim federal moguls website states 95-up Lincoln heads have the same valve seal as 96-up cobra. Well....isnt the Internet nice! Here you go guys Hopefully the pic is clear. Notice the valve guides over all diameter from the top down to the spring pad. Youll see the guide is machined from the top, down to about a 1/16" of the pad. Cobra heads were not this way (and those valve seals carry from 96 all the way to the end, iirc) Cobra valve guides had no O.D. machining. Why the lincoln did baffles me.....I believe an available valve seal, possibly for another make, already in production was used and the guides needed to be machined for proper fit. Well....when rebuilding the heads, folks would grab a set of valve seals they thought were correct. Not knowing the feel of a valve seal press over the guide, they knew no different. Only to have oil sifting out the valve guide. The B heads have 2 seperate intake ports. IMRC valves that sandwich between intake and head. cobra Lincoln At port entry on the head, nethier port resembles one another offering 2 completely different ways to induce incoming rush into the cylinder. Primary port being square at the port entry, secondary port being oval. I state primary because the intake head combo had motion runner controls over the ports. This basically was a throttle butterfly over the secondary port blocking it untill a certain rpm was reached and them opened by an actuator allow free flow into both ports. This runner control allowed for better emissions and greater low rpm driving torque. Great idea thats still used today! All the 3valve engines incorporated the idea as well.