Would I need the larger calipers also?
No.
But calipers for a 2500 with the larger piston will work. A bolt-on.
Use with the 1500 pads. The tabs have to be
carefully bent out, in order for them to fit & hold inside that bigger bore.
A fairly common upgrade with more than a few discussions here over the years as to the pros & cons.
A mod I haven't done. Yet. Maybe.
While you're at this, one mod that I would recommend is the GMT800 master cylinder swap.
Also...much discussed. Lotsa techno-geek stuff as to why or why not.
This I have done. Seat-of-the-pants, (foot-of-the-pedal?) it is an improvement, no matter what some 'hydro-engineer' says about why it's not a good idea.
The mod took a lot of the mooshieness out of the pedal. A common 400 complaint.
Not perfect, but certainly much better than a 400's OEM M/C.
Look for rotors & drums with a high nickel content.
Pricey initial outlay, but way cheaper over the long run. They will last so much longer than the off-the-shelf jobbers, including OEM GM replacements.
$60.00 rotors last me about 8 months. Junk. '0' lathe turnings.
$250.00 rotors last me 5+ years. 3 turnings.
H/N/C drums could possibly outlast the truck!
I like ceramic pads. They're low dust & they last.
Little harder on the rotors, but with a better nickel content, not too much of a concern.
They take a block or three to get up to temp, depending on the season. Be aware & it's not a biggie. After a while, it just becomes part of driving the truck.
With all this done, pads up to temp, & my '98 easily dips into double digits in feet off of 60mph panic stops.
*ABS deleted.