Byte 04: Cursory glance suggests that bit 7 (80) indicates to DO a status raise based on byte 05. I’m not sure why certain items have 80, indicating to raise nothing, but this may be because if bit 7 is NOT set it does something else.
Example:
HardLeather:
byte 04: 05
byte 05: 20
Obviously, HardLeather doesn’t give +5 VIT, and all the stat-up equips that I’ve seen so far have had bit 7 set–PowerBelt, for example, has 94 and 01, indicating +20 STR.
LaserKnife: — 0A 0B
CeramicSword: - 0D 01
TwinSword: ---- 0A 09
Osc-Sword: ---- 0F 09
JackalSword: – 10 11
CometBlade: — 19 03
Obsidian: ----- 19 03
Kusanagi: ----- 19 03
Murakumo: ----- 0F 03
DragonSword: – 1E 01
SilverMoon: — 19 03
GoldenLion: — 19 11
Lordstar: ----- 14 0B
KillerRifle: - 19 08
EagleGun: ---- 0D 0A
SniperRifle: - 0D 0A
BehemothRifle: 0A 2A
AGUNI-MBX: — 10 2A
DuelGun: ----- 14 2A
ZenGun: ------ 14 1A
LethalGun: — 14 2A
HandBlaster: — 07 0A
LaserCarbine: – 0D 0A
HyperBlaster: – 19 0A
BeamCannon: ---- 0F 28
LightningCannon: 0F 28
SonicCannon: — 14 0A
WaterCannon: — 0A 28
JunkBazooka: — 05 09
LightVulcan: — 08 2A
MachineVulcan: - 12 2A
Thunderbolt: — 14 28
FlameThrower: – 14 28
BoltThrower: — 14 28
IonCannon: ----- 0F 0A
GrainCannon: — 0A 22
HG-Cannon: ----- 1E 0A
GhostCannon: — 0A 10
LightBazooka: – 0F 08
HEATBazooka: — 1E 08
HyperionBazooka: 28 08
BODDYBazooka: – 08 29
MissilePod: ---- 0F 09
BigMissle: ----- 14 09
SuperMissle: — 19 09
LaserCannon: — 0C 05 (at 2A330)
RailCanon: ----- 2D 02
LaserCannon: — 05 3C (at 2A49C)
RepairPack: ---- 14 0C (at 2A560)
OctopusBoard: – 19 0B
NakajimaBoard: - 1E 02 (at 2A598)
NakajimaBoard: - 0F 0E (at 2A5B4)
V-Special: ----- 0F 7F
V-System: ------ 0F 7F
JunkParts: ----- 03 03
RailCannon: ---- 19 A8 (at 2A624)
MemoryBoard: — 19 04
SecretBoard: — 0F 04
HardLeather: – 05 20
ArmorVest: ---- 05 20
BlueElf: ------ 0F 14
PlutoArmor: — 14 30
SprigganSuit: - 19 07
GolemSuit: ---- 1E 01
YolkHat: — 01 0C
MirrorGlass: 19 0C
LeatherGlove: 05 01
SH-Armlet: – 14 21
LeatherBoots: 05 02
Catsocks: — 05 02
SH-Anklet: – 14 22
SanctuaryStone: FF FF
That’s all the items that don’t have bit 7 set in byte 04. Bytes 04 and 05 are listed (in that order.)
Well, I included SanctuaryStone for gits & shiggles. 
EDIT: Well it seems nothing on that list has byte 04 set to 00…interesting? My dunno…
