12a blocks-differences between yrs?

[RobMatthews]

As the title im in need of some simple answers please!

The 12a block found in my rx4 originally had the 6mm carbon seals and I notice the later 12a block I\'ve also got has different/bigger ports,
Is that the only difference befor turbos got added?

Basically im shopping for new/good housings and possibly rear iron and need to know what years  can go for?

Thanks Rob

[HaywardRotary]

Through bolt pattern is different on the early RX4 12a from the 1st gen RX7 12a.

[RobMatthews]

As in the early 6mm tips block? so all the other 12a after that are the same? up to the turbo\'d engines?
You got any?