GPA P 5219942 in Rob's second post above ("Google") is from 21 A Gp MC Pool (21st Army Group Movement Control Pool), as testified by the Unit Serial 39609.
The 5 KINGS GPA of LCT 610 (212) also displays a Unit Serial (24774), just above the "T(4)" part of the "212 LCT4" marking on the "front bumper" - or rather "bow"

. The AoS "67" is on the right hand side of the windscreen, while the chalk number "21" is some sort of individual vehicle landing number - not quite strictly adhered to as there are several discrepancies in the sequence (e.g. "24" Sherman III No.11, "26" No.10 BALACLAVA, "30" No.69...). There should be a WD number somewhere, as well as (probably) a Beach Group anchor?
Here are all the GPA listed in the Landing Tables for GOLD (1st & 2nd Tides) and SWORD (1st Tide) (I don't have those for JUNO). Notice that the description varies depending on the unit issuing the table!
GOLD - total = 5x GPA
Det Mov Control Pool 21 Army Group
1x Amphibious Jeep H+90 Jig Green East side 39609/2163 LCT (4) - 3 Veh. Parties
1x Jeep Amphibian H+90 King Red 39609/2555 LCT IV - 3 Veh. Parties
6 BORDER
1x Amphibious Jeep + 1x 3 Ton GS H+3½ King Sector 24844/2183 LCT (4)
2 HERTS
2x Jeeps Amphibian H+120 King Red 23074/2562 LCT IV - 2 Veh. Parties
SWORD - total = 18 GPA
'F' RN Beach Commando
1x car 5 cwt 4x4 (amphibian) H+45 QUEEN WHITE /211 LCT(4) - 1 Veh. Party
17 RN Beach Sig Sec
1x car 5 cwt 4x4 (amphibian) H+45 QUEEN RED /221 LCT(4) - 2 Veh. + 4 Marching Parties
'A' Coy 5 KINGS
1x car 5 cwt 4x4 (amphibian) H+45 QUEEN WHITE 24774/212 LCT(4) - 2 Veh. + 23 Marching Parties, 2x handcarts - part 1st pl
'C' Coy KINGS
1x car 5 cwt 4x4 (amphibian) H+45 QUEEN RED 24774/221 LCT(4) - 1 Veh. + 4 Marching Parties, 1x bicycle, 1x handcart
HQ 5 KINGS (HQ 5 Beach Gp)
1x car 5 cwt 4x4 (amphibian) H+120 QUEEN RED 24774/301 LCT(4) - 1 Veh. + 2 Marching Parties - Adjt RSM
1x car 5 cwt 4x4 (amphibian) H+120 QUEEN RED 24774/303 LCT(4) - 2 Veh. + 5 Marching Parties, 1x handcart - incl 2IC batman and sjt, Padre, IO and IO's batman
21 FDS
1x car 5 cwt 4x4 (amphibian) H+120 QUEEN WHITE 36004/296 LCT(4) - 1 Veh. Party - to proceed to QUEEN RED on landing
1x car 5 cwt 4x4 (amphibian) H+120 QUEEN RED 36004/304 LCT(4) - 1 Veh. Party
20 FDS incl Surgical Team
1x car 5 cwt 4x4 (amphibian) H+120 QUEEN WHITE 36003/297 LCT(4) - 1 Veh. Party
1x car 5 cwt 4x4 (amphibian) + 1x 3-ton GS 4x4 H+120 QUEEN RED 36003/305 LCT(4) - 3 Veh. + 7 Marching Parties
HQ 101 Beach Sub Area
1x car 5 cwt 4x4 (amphibian) H+240 QUEEN WHITE 36175/337 LCT(4) - 2 Veh. + 4 Marching Parties
HQ 101 Beach Sub Area Sigs
1x car 5 cwt 4x4 (amphibian) H+240 QUEEN RED 39096/348 LCT(4) - 3 Veh. Parties - incl 1 offr for recce
1x car 5 cwt 4x4 (amphibian) + 15 cwt GS 4x4 HUP H+240 QUEEN WHITE 39096/351 LCT(4) - 8 Veh. + 13 Marching Parties, 2x handcarts WT
S & T rep incr (5 Beach Gp)
1x car 5 cwt 4x4 (amphibian) H+240 QUEEN RED 36108/345 LCT(4) - 4 Veh. Parties
CRASC 21 L of C
1x car 5 cwt 4x4 (amphibian) H+240 QUEEN RED 36108/348 LCT(4) - 3 Veh. Parties
Nucleus BAN Sec
1x car 5 cwt 4x4 (amphibian) H+330 QUEEN SECTOR /381 LST(2) - 2 Veh. + 22 Marching Parties, 3x handcarts WT, 1 bicycle, 1x MC - for MBSS
L/T Sec
1x car 5 cwt 4x4 (amphibian) H+360 QUEEN WHITE /402 LCT(4) - 3 Veh. Parties
1x car 5 cwt 4x4 (amphibian) H+360 QUEEN RED /408 LCT(4) - 3 Veh. Parties
Michel
remove "truck" from email address