In QB64, you can use: DEFLNG L
So now any numeric variable that starts with "L" or "l" will be long. Funny though, by default any undefined numeric variable is already long. This makes me wonder why we haven't seen a _DEFINT64 new QB64 keyword yet, as back to your question, there is only DEFINT available in QB64, from the old QB45 days.
Assigning with TYPE is something I seldom do, but I would think you would have to type each variable, and not just the starting letter of any variable, but I might be mistaken.
Pete