Add new radiator off of existing wall unit?

Bucky

Hi all, now that the radiant system on the 1st floor is humming along, time to turn my attention to the "old" part of the house.

On the third floor, a prior owner had added a dormer to eliminate the 2' ceilings that existed due to the sloped roof (this is a 200+ YO farmhouse). They did this for almost the entire width of the room and left about 8' on one side (converted to a small bathroom) and 3' on the other side (now a small 'closet'). The remainder is now the master bedroom of about 18' wide.

The issue with that is that both the existing radiators were left where they were- one in the bathroom (good!) and one in the 'closet' (bad!). It leaves the bedroom portion with no direct heating source and it can get rather chilly. Now this is a job that I really don't think will be a DIY and I'll have to hire someone (a rarity for me), but I want to figure out my options and come up with a plan first. I think what I'd like to do is add some sort of baseboard radiator in the bedroom portion fed off of the loop with the closet radiator. I would just need to poke a hole in the partition wall between the closet and the bedroom and feed off the input sides of this existing radiator and run something through the wall and attach to some sort of baseboard unit. I would want the new baseboard unit to be first in the loop since it's not that important to heat the closet

I've attached a picture of each side of the existing rad. The inflow (valve) side is on the same side as the bedroom, so that's a plus. Do you guys thing this is something a competent plumber could work with without tearing the house apart? (I also see there's significant rust below the valve-something that could also be remedied at this time). (And now that I try to follow the pipes, it looks like that valve side runs horizontally under the floor before it hits the riser) And is there any kind of pex connection I could use the new baseboard on the other side- and what kind of baseboards are available these days? I'm guessing like 5K BTU would do it for the room, but I guess I should do a little more heat loss analysis, although kinda hard to get accurate when it gets the latent hit from the two side rads). Thanks.