Hi gruberd,
The dimensions of our E-Z Track Figure 8 Track Pack (item no. 44487), with 18" radius curves, is 39" x 76". So it will be a very tight fit inside your O-27 oval, but it is possible.
https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=258_366_369&products_id=5748
The dimensions of our E-Z Track Figure 8 Track Pack (item no. 44487), with 18" radius curves, is 39" x 76". So it will be a very tight fit inside your O-27 oval, but it is possible.
https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=258_366_369&products_id=5748