This issue is a variant of Thor (Marvel, 1966 series) #231 [Regular Edition].
Per Nick Caputo John Romita provided extensive revisions to the cover, particularly on the creature and Thor. The unaltered cover was used in the Italian reprint Thor e i Vendicatori # 149. Possible Giacoia inks also per Nick.
Letters page includes a house ad for Vampire Tales and Marvel Value Stamp # 83 (Dragon Man).