I can't start to count how many marble angels I have right now. Angels generally do not do very well below 80F. I keep younger angels, including marbles at a minimum of 84F. Angels can handle quite a bit of heat, I've had them well into the 90's with no adverse effect.
That link has a couple discrepancies, "The Marble Angel is one of the most hearty Angel Fish, making it one of the best choices for someone wanting to experience Angel Fish for the first time." and "Marble Angel Fish are not the strongest fish." In actuality, marble angels are one of the stronger strains. Any strain will be weak if improperly bred. Blacks, especially double darks are one of the weaker ones out there, due to the inbreeding needed to get that color. Marbles have been around for quite some time, they tend to be stronger than most.
My angels must not have read the part about needing a pH from 6.8 to 7.2. They live, spawn, & hatch in 7.7 pH.
I would slowly, over 3 days raise the temp, get it to at least 82F. Avoid bloodworms, they tend to constipate. You don't need this at all right now. Brine shrimp are a good choice, what you are trying to do is get the temperature up to a normal range, which will increase metabolisim. Increase in metabolism means an increase in appetite, which is needed if some infection did set in due to the temperature drop.
First priority should be dealing with the temperature drop, which put the fish into shock. Once that is dealt with, infection, if any, will be easier to deal with.
Tolak