I have been using the 40GB-FUP-999 plan for a few years now. RCOM, in their promotions, promised to carry forward the old plan post migration.
RCOM is not offering these plans in 4G. But, since 1X is working in your town, you may be able to get 40GB plan with a fresh CDMA connection. And later migrate the said connection to 4G.
Subject to compatible frequency bands, 4G sim card should work with most unlocked LTE devices.