If you have a little time just buy a 160 for a SBC and trim it down, that is pretty much what I do. Any part store will have it in stock and takes a few minutes with a grinder to knock the edge down.
In the summer I just run the thermostat housing and the car stays really cool and in the winter I will put a 160 in it to hav some heat but I found that is not real necessary because it does not get crazy cold here and the car does get plenty warm to have heat.