I have a 13b (6 port) Gasket kit I bought a while back to build a motor that I never went through with. I'm wondering if there is any real difference in the o rings and gaskets to close the motor?

Obviously there are differences in the paper gaskets. But I'm not concerned with that. Just the o rings and jackets to close the motor.

Basically, could I use this kit to close a 12a or a Renesis?

 

nope.. the 86-91 FC 6 port kit can however be used as basis to rebuild any FC engine or any FD engine
earlier engines have coolant grooves in the housings ( as does rx8 ) and use different sized coolant seals

 

By different size, do you mean thickness or depth?

And are the waterjackets the only major concern? I know there were material changes to certain o rings. But I'm only concerned with fitment.

 

Today I took a few measurments. I measured the inner and outer wajer jacket grooves depth and width on an Renesis housing, 13b 6 port (FC) plate, and a GSLSE housing. The Renesis and 6 port were exactly the same. While the GSLSE were slightly smaller. Just a few thou.

This lead me to believe that 1st gen, (12a or 13b) jackets are sightly smaller and should be only used on those motors. While all others can interchange.