Sounds like a 4G54 motor,
but can't tell without a Full model & serial number, you can get one from almost any quality industrial motor rebuilder, only thing is you'll end up eating the core charge since the old motor isn't rebuildable.

You can have one swapped and running in 8 to 12 hours although most shops charge 16 to 20 hours for a R&R.

When you start trying to mix this and match that from the automotive world you have to know your motors and what will and won't work & most car parts counter monkeys will only give you a "Deer in the headlight look" when you ask them questions about forklifts,
I've found that most of them can't spell "Forklift" much less tell you what goes where.

Spend some time doing internet searches for suppliers and also get your trucks full model & serial number and call a dealer and get their part number, you can get these long blocks for about $2400 to $2800 plus freight. The motor model and serial number will be on the left side of the motor just between and below #2 & #3 spark plugs.