It's very rare for LRB's to have been countermarked.
Both of these have cm's of a tetrastyle temple, similar to Howgego 286 from Panormos, Sicily. Interestingly these two coins were issued about fifty years apart and have the same cm, maybe done around the same time or completely separate times. Both coins have considerable wear. Were they worn before the cm's were applied or did they wear down after cm'ed circulation.
The Howgego 286 cm was also applied to 1st century coins like Augustus or Tiberius...these two coins were considerably later. So several questions with not many answers.
Gallienus BI Antoninianus. Rome, AD 264/5. GALLIENVS AVG, radiate and cuirassed bust right; countermark: tetrastyle temple / SECVRIT PERPET, Securitas standing to left, leaning on column, holding sceptre; H to right. RIC 280; C. 961; MIR 595w; for countermark cf. Howgego, GIC 286 (Panormus). 2.99g, 22mm, 6h.
Constantine I Æ Nummus. Rome, AD 312-313. IMP CONSTANTINUS P F AVG, laureate, draped, cuirassed bust right; countermark: tetrastyle temple / S P Q R OPTIMO PRINCIPI, legionary eagle between two vexilla, RQ in exergue. RIC 349a; for countermark cf. Howgego, GIC 286 (Panormus). 4.12g, 22mm, 6h.