1987 GMC Suburban- Having issues starting

Ok I have been through a ton of topics on here trying to find anything as close as possible to the prob we are having and have found very little thats close and was answered. Here's the story start to finish. This is a GMC suburban 1500 sierra classic 350 motor. I was driving down the road the other day and it literaly just shutt off. We assumed it was the alternator since there was no rumble sputter smoke overheating or anything else. SO we had it towed home and changed the alternator which we also had tested. The alternator was definitely bad but for some reason the burb still would not start. So we changed the starter since when we went to start it it would basicly click. Had the cyllanoid switch checked and it was fine. He went (hubby) made sure the new starter was shimmed up right and everything. Ok so it still would not start. Then we had the battery checked. Well it needed to be replaced. Got a new one. The starter engages the flywheel but won't turn it. Now we are down to the flywheel possibly being locked up. I am soo hoping this is not teh case. Motor isn't locked and the burb will shift and you hear the click on it when moving the gearshift. Forgive me if I do not explain enough but I am trying to give as much detail as possible. I want to elimate any possibilities of smaller causes before having to take this thing to the shop. This is literally the first time we have ever had trouble out of this vehicle. Double checked oil and trans fluid as well. No water in the oil or crud. Transmission fluid isn't burnt or smelly. All lights work fine. No burnt out fuses went ahead and rechecked them as well. Please would appreciate you advice on this. Hubby doesn't have enough tmeto actually replace a flywheel so even a rough estimate of how much that usually costs would be helpful. Well I am off after writing this book. I look forward to your replies.
Lively :roll: :lol: