Originally Posted by FoxChassis
"XXX" does not mean roller block. Non-roller blocks also had that casting mark. It means nothing.
FKSE is not a valid engineering number. (The "K" is not actually a K.) Check it again. It's probably a "F1SE". The F1SE block is very common, and it is indeed a roller block. It was originally engineered for a 1991 Thunderbird (F1S = 1991 Thunderbird) but it was used in other models. The '91+ Mustang also used that block.
If you want to know exactly what vehicle the block came from, you need to locate the partial VIN that is stamped on the flat pad on the top-rear, right behind where the (lower) intake would bolt down.
Fox: I'm having a hard time trying to id what I have. I too have XXX under the intake (and just one X on the other side) and found this older thread thinking the X's may mean something. (My current thread is: "1980 V8 - what is it?").
Anyway, the numbers I see stamped on that flat plate at the rear of my bock are: BB 13808. The last 08 is very faint, and may be wrong. But the BB, then a space, then 138 is quite distinct. If you could point me in the right direction with this and the other numbers I've listed in my thread, I'd appreciate it!