Coming late to this party. (Again!)
But I toss this in for good measure. I back dated the earlier AFV Korean War Long Tom kit using one of the PSP resin wheel sets then available from Scale-Link in the UK.
This one also has the aluminum turned barrel plus a big carpenter’s nail tucked into the breach to counterbalance the weight of that barrel!
The Mack NO did not require a Limber to tow the the 155mm. In fact the truck had greater tractive effort when hitched as you see here. The M2 and M5 Limbers were often towed behind the gun when using the Mack NO. (That’s really what that pintle on the back of the gun is for.) Once the gun was emplaced the Mack might be off doing an ammo run, so later a HST might next have been assigned to move the gun and the Limber would then be required.
Seen below- Ammo Train: Two M23 8-ton Ammo Trailers being pulled by yhe Mack NO ~ Built by Utility Trailer Corp. ~ still in business today!
Photo above; copyright Ampersand Publishing & David Doyle
My attempt at the M23 Ammo Trailer