In 89, those would be 7A heads. The ports are exactly half the size of 5As. 5As would allow you to use aftermarket intakes and they flow a little better.
The heads should have the casting number on the top of one of the exhaust ports. Scrape the grease off and it will tell you what heads you have. If you can get it to breathe, a 307 is a pretty nice engine. It has a roller cam and the head designs are pretty fuel efficient.