Can St Louis ribs be substituted with same results. Not familiar with cooking ribs and see St Louis readily available in market.

Make sure you pull the membrane off the back before doing anything else. ;o)

Yes, it will work although you will have to increase the cook time probably by 60-90 minutes.

Here's an explanation on the different pork rib cuts:

https://www.smokedbbqsource.com/types-of-pork-ribs/

Basically St. Louis ribs are spare ribs with the rib tips and other meat flaps trimmed off.

Spare ribs have more bone and fat than baby back ribs which are closer to the animal's back hence the name. Baby back ribs are leaner and have more of a tendency to dry out. This won't be a big problem in this recipe since the meat is wrapped in foil which helps retain moisture.

If I tried this recipe with St. Louis ribs or spare ribs, I'd probably cook 4 hours and then check the meat texture for desired consistency. Very few people prefer a chewing gum texture. Some like it softer but with some resistance and juiciness. Others like that classic "falling off the bone" doneness.

It's up to you to cook your ribs to the desired texture for your dinner table guests.

Best of luck.