Main Drain Cover Replacement Help

34 year old pool recently drained, but for years we understand there has not been a drain cover on the bottom of the main drain nor the spa.

I have linked to a picture of the main drain with some measurements and wondering if there is anything special I need to know about finding and replacing the pool. The pool was build by Blue Haven pools here in Texas.

Is there a "generic" replacement that I can use? I'm not even certain what type of screws I should used.

https://4tipaw.bn1.livefilestore.com...Raw.jpg?psid=1