There is no way to electrify any trackage by end of Dec 2024. They might get some electification CAT installed. But a location for MBTA substations probably have not been acquired. The present Amtrak sustation(s) probably has extra room FOR additional transformer(s). It has been noted elsewhere that Amtrak's does not enough capacity to handle the additional load of MBTA.
Amtrak aways has enough power capacity that if a substation goes off line that one or more (near) stations can provide enough power to allow any regular or extra loads. Now if Amtrak already has specifications for the needed NEC substations. They might be able to be ordered, constructed, tested, delivered. tested, Certified, & put ito service for the NEC and Fairmont line.
However, if not available NEC specs and for the Newbury / Rockford line there is no way power substations can be ready by Dec 2024. Besides getting real estate, Envirometal review ( substations make some noise which has to be specified ). Also cooling fans have to be high enough to avoid any possible snow, Amounts of regenerations imputs have to be specified and more items .
. Here is a link to all items that will be needed in specs. Then get a building slot time in costruction plant. You do not buy these substations off the shelf.