1> Any reason why they can't be cleaned up and re-painted? If they can't be refurbed, measure the distances of the fins from the floor and wall, and check against he dimensions of the SlantFin parts to see if it fits:
2>Don't bother adding bleeders unless you have chronic vapor-lock/low-flow issues.
3>At 80' of total plumbing including fin-tube it doesn't take a monster pump to get the minimum 1gpm of flow. But it helps to have the whole picture in front of you- total length of pipe, the number of ells & tees, the published "head" of the toe-kick heater, the pump that's driving it, and the boiler's head, then do the math or look at the pump's gpm vs. head or equivalent-length of the plumbing.
Before you even look at the covers, what's the boiler, and what are the total amount & type of heat emitter on each zone? When systems get cut up into zones like that it can take a toll on the boiler if each zone isn't independently capable of emitting a large fraction of the boiler's output at the high limit temperature, sometimes resulting in 10+ burn cycles/hr on zone calls. This is bad for efficiency as well as for maintenance & longevity, so before hacking on it, do at least the crayon-on-napkin math- you may want to be doing more/different than than adding vents or nicer looking covers.