take your original flights and check in early to get on the SB list. dont check bags. get to EWR and book it to the earlier flight. ask how it looks to get on, and that if you could get on, what the FC list looks like.

they will have to clear you in coach and then upgrade you if seats are available and there isnt already a list that your cant trump being gold on a B fare.

id say you have a decnet chance on your original flight though.

you could also ask the agent at MHT about the earler flight. tell them you want to get mco ASAP. they may rebook, but again, be sure you'd good to go for FC or forget about it. your 752 may have AVOD in Y so it may not be that bad.