See if it rotates. The A4 does have a hand crank, and there's usually an access hole in the settee right in front of the engine. Don't try to start it with the crank, pull the plugs and see if it rotates. If it rotates, make sure there's oil in the pan, squirt some oil in the plug holes, then just basic gas engine diagnosing: suck, squeeze, bang, blow.. The starter needs to spin it. You need fuel from the carb. You need compression. You need spark. 1950s basic mechanics. (Well, its a boat engine, so you need cooling water too if it starts to fire.)What would be the best way to check what is wrong with the engine? I got the boat from the third party and they do not know what exactly happened. Just saying it is "frozen". I will be visiting the marina where the boat is and thought of removing the engine and taking it back home to see if it can be repaired. Will I need a crane to get it off the boat (it sits on the cradle)? Besides the engine itself what other parts will I need to remove/take home?
Pulling a Catalina 30 A4 is easy for a boat engine - remove the counter, unbolt the engine and pull it out the companionway. In the water the boom (supported by a halyard at the point of lift) is fine to get it out. I'd be cautious doing that on stands cause when you swing the boom out to drop the engine off the boat, that's a lot of weight on the side. Wouldn't want to tip the boat over - so on the hard I'd use a crane/backhoe/4 big guys/whatever.
For all things A4, moyermarine. Plenty of rebuild threads on the forums there.
That's a looooooooong way to go in a C-30. You'll need an engine in good condition to go through the river and canals. You'd need jerry cans of fuel too. Range under power is around 50-60 miles if you're engine is running right. I'd just buy a boat already closer to you.