Moving radiator closer to wall

Pitch is not paramount. Anything close to level in either direction is fine.

Yes what you want to do is fine. But do what @Jamie Hall says above and pipe the radiator from below if it can be accessed there. If not, and since are are doing some carpentry anyway, pull up some of the floor and pipe it from there.

No. The valve is connected to the radiator spud with a union — and that is a matched pair. The one half of the union is part of the valve body, and the other half is one end of the spud threaded into the radiator.

Now you might be able to get the spud out of the radiator and thread a pipe in there, and then a 45 and thread the spud into that 45. Then again, you might not. Spuds aren't all that easy to remove from old radiators…

Or you might take the spud out and the valve off, and get a new valve and its matching union connection and do the same sort of thing, only with new hardware.

Bottom line: in order of relative difficulty. Easiest thing to do is redesign the bench so that the radiator fits. Second, extend the runout under the floor and come up with a new hole to meet the new radiator location. Third, monkey around with the spud and radiator valve and come up with a new connection.

You're going to be happy you did I think. While you're down there make sure the pitch of the horizontal section of the runout under the floor is away from the radiator. THAT pitch is paramount

Depending on how much space you have on the riser you could replace it with 2 45's and some nipples to offset it closer to the wall. You may not have enough access to do that because the end of that runout probably is above the foundation.

nope, the valve is part of a integrated assemble with the union than connects to radiator. You can remove the valve and replace with a straight through radiator valve with new spud. Add a 90 at the pipe then a street 45 and finally a short nipple to valve.
make sure you maintain the runout in the pipe.

Or the short version; what @Intplm. said.

Aluminum foil over a thin piece of sheet metal (or even wood or cardboard) the same dimensions as the radiator can be placed against the wall and will reflect nearly 100% of the infrared light emitted by the radiator back into the room. I think about 80-90% of the heat delivered by the rad is through convection, so only a small portion is infrared, but at least it won't be wasted through your walls.

Just asked ChatGPT this question, and it told me 31-41% is radiant off the bat. Radiant is calculated using Stefan-Boltzmann law, and Newton's Law of Cooling is used for convection…but then I started changing some of the inputs, white paint, silver paint, radiator design. The one in the picture is painted silver, and GPT thinks the radiant is only around 10-15% in that case. If it were unpainted cast iron, it would be as above, white paint would lower it slightly to 28-37% because lighter colors are worse radiant emitters, and black would increase it to 39%. I remember reading Dan's article on this https://heatinghelp.com/systems-help-center/metal-paints-and-radiators/ . But this is the first time I've actually seen the math, and I thought this was pretty cool. I wouldn't have tried to do the calculations just with the ASHRAE handbook equations, but AI sure does make things easier…