Victor

A bit of a late reply (just shy of a decade), but yes I am keeping the site going. I am always adding material like the assorted rulers pages- http://www.constantinethegreatcoins.com/Rulers/ and a page about a new reverse for Constantine http://www.constantinethegreatcoins.com/VICTORIA/ plus some pages get udated, my unofficial coins page had a pretty large overhaul recently http://www.constantinethegreatcoins.com/barb2/ a few years ago I also made a new homepage

It’s Valentinian I with a SECVRITAS REIPVBLICAE reverse from the Siscia mint

It's pretty blurry, but I think that you have Licinius I, like the one below.

You are correct that it is Arcadius. The third letter in the obverse legend is an A, which means it can only be Arcadius-- D N ARCADIVS P F AVG

Your coin is Valentinian I with a GLORIA ROMANORVM reverse from the Sirmium mint, struck in A.D. 364

Better late than never Crispus A.D. 321 CRISPVS NOB CAES; laureate head right. CAESARVM NOSTORVM surrounding wreath enclosing VOT V. In ex. T ✶ in crescent A RIC VII Arles 241