Verlinden mades two resin, full M4A3 Ford GAA engine plus engine compartment kits. The 1st one is number 1136 and included a replacement engine deck. It's OK but there is no detail whatsoever on the underside of the engine deck grate. Kinda defeats the purpose no? It was designed for the Tamiya kits.
The newer kit is #2644 and omits the engine deck. It's designed for the modern Asuka/Tasca kits which already have nice, separate engine deck grates.
My advice for you is to get the cheaper of the two (2644 or 1136) and beg and plead for someone on the various AFV classified sites, to send you a pair of M4A3 engine deck grates. Then add the duct work beneath the doors yourself. (Formations Models (currently not in production until after Sept 1) has a replacement set of engine grates plus the duct work beneath them.
But my most serious advice for you is this: just build the kit. Don't worry about adding a resin engine. You want to get something done. If you start getting bogged down now, acquiring items and adding weeks/months to your very first build -- your momentum will grind down to a standstill. Finish the Academy M4A3 and take the money you'd use for the replacement engine/engine compartment and buy another injection plastic kit that already has a nice open-able engine compartment. There are plenty out there. Just post again and we can advise you.
Don't do the engine. Finish the Sherman!
(one bit of advice on the suspension: place the kit, without tracks, on a level surface and glue all twelve road wheel arms in place -- don't let them rock back and forth.)