Madape,The learjet cockpit isn't all that cramped. It just looks like it. It's a good fit. The Learjet type rating covers the LR20 series, and the LR35/36. These all have similiar sizing in the cockpit, though the 20 series are a little smaller and have a little less room up there. Later lears such as the LR45 have much more room up there, and are more comfortable, as well as nearly a stand-up cabin.
FL230 is low level for the learjet. It's not so bad in the LR35 in that picture, but a real killer for the 20 series. At that altitude in a LR24 or LR25, you can watch the fuel gage wind down...you can see it move.
Are those the rosen sunvisors in that picture? It looks like a better system than the standard visor system, with the ability to block the sun near the windshield center post...something you can't do on the standard LR arrangement.