"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.
1979-1993 Fox Capri and Mustang VIN Decoder: foxchassis.com
Wanted (Dead or Alive): VINs, Vehicle Certification Labels, Buck Tags, Build Sheets, Window Stickers, Owner Cards, Warranty Tags, History 999 Reports, Invoices, Axle Tags