Jammed deck lift

Here is a parts breakdown schematic that shows the manual lift deck lever and the associated parts.

Simplicity 1693969 Conquest 16HP Hydro and 44 Mower Deck Lift Group Manual...

You should have a lever to lift the deck 'UP'; and there is a hand-wheel adjustment to keep one level.

Sounds like you have jammed linkages which raise and lower deck, you can try this which usually works best with assistant.
With engine off, shake the deck vigorously (up,down, back and forth) while try to raise deck with lever.
Check for worn or damaged arms, springs, deck mounting points, etc and repair or replace.

Inspect the linkage connecting the lever to the deck. That's what I would do.

If this is a manual engagment system all the lever does is to pull a jockey wheel into the back of the belt to tention it thus starting the blades to turn, so either the cable is jammed that pulls the jockey wheel in, or the jockey wheel arm is seized and needs freeing off to allow the jockey to to move to the relaxed position.

There is one thing that commonly causes the deck to cut unevenly. The mandrel/spindle has one of the ears cracked. Probably have to remove deck to get a good look at all of them.

If you want antiscalping wheels for your deck, they can be purchased and added to the machine.

I hope this helps you out.

There are 4 nuts on the top of yoke that holds the bars.
Do up the front ones first and then do the rear 2 to grip the bar tight.