As stated above, unless it is a very serious motor you will not need an oil cooler for street use.
Having said that, there are at least 4 possible options and then probably some.
Vertically on driver's side next to radiator as per TI Super/GTA.
Vertically on the driver's side in the battery box area with rear mounted battery or small battery near firewall if car is run w/o brake booster. TI super style inner headlight delete with it?
Horizontally in front of the radiator with the lower edge of the cooler lined up with the lower edge of the grille - I have a 9 row cooler mounted on one car like that. Works particularly well with later radiator set-up.
Horizontally on driver's side in front of radiator tucked into front valence. GTA-style vent cut outs necessary or late Nuova front valence with cut-outs - I have a 19 row cooler mounted on a car there. Upper edge of cooler comes up to lower edge of grille.
Oil radiator should be mounted so it does not drain itself, e.g. inlet outlet on top. Dash 10 fittings are preferred for flow.
Adapter is available among others here:
Oil Cooler Sandwich Plate for early cartridge type oil filter | Classic Alfa Romeo spare parts and accessories