Ok I see your point, the book came in today.
Sorry you ordered it before reading our responses. Still you can salvage something out of it, right?
They could use grav technology for the tanks and combat cars right?
Gravitics instead of "blowers" is a very big change. Not an insurmountable change, mind you, just one you need to be mindful of because of the consequences to the effect of terrain on movement.
The tanks and combat cars in Drake's books still require bridges and fords while also tending to avoid swamps and marshes. As hovercraft, they need a hard surface, or a hard surface somewhat below a "mushy" one, to "push" against. They aren't the low mass/wide footprint, water-crossing, hovercraft we use as rescue vehicles, landing craft, or ferries. They're high mass, narrow footprint, bricks which only "work" as hovercraft because of their fusion power plants. (IIRC, Drake has written that his "blowers" are actually physically impossible.)
Thick vegetation also impedes the movement of Drake's Slammers. They can bull their way through saplings and the like just as current armor does, but, in at least two stories, they actually use their artillery to set forests on fire in order to provide lanes for movement of tanks and combat cars.
Compare all that to gravitics. Grav tanks
fly. Grav tanks can
reach orbit.
Grav vehicles can cross anything anywhere no matter how "fragile" or "mushy". The river that would force the Slammers to build a bridge, the bays, lakes, and ice sheets that would force the Slammers to make a detour, and the seas and oceans which would make the Slammers use other transport do not effect grav vehicles at all. Also, while a blower has to bull or burn it's way through a forest or other dense vegetation, a grav vehicle can simply "hop" over it all or "fly" over to "land" in an otherwise inaccessible clearing.
Imagine playing a wargame where one side must take into account the effects on movement of river, wood, lake, and other similar hexes while the another side can simply ignore all of that and you'll begin to understand just how big a difference there is between gravitics and "blowers".
There is no need for powerguns at all.
Where gravitic technology makes tanks in "Traveller" more dangerous because it provides much more "agility", power gun technology makes the weapons in Drake's books more dangerous because it's much more "cheap".
Look at the various fusion guns in "Mercenary", they all require fusion plants for "ammo" while Drake's 20cm main tank guns "only" require those copper-laced "wafers". It gets even worse with personal arms. The Slammers carry pistols, submachineguns, and rifles whose best "Traveller" equivalent for damage are the PGMP and FGMP. Both those "Traveller" weapons require battledress and power packs, but the Slammers carry their versions much like we carry chemically powered slug throwers today.
Sure, the Slammers need actual ammo where "Traveller's" various plasma/fusion weapons can run off power sources, but power guns mean the Slammers are carrying more "boom" for much less "buck" and much more often than any "Traveller" merc outfit could manage.
Years ago, I tried recreating the Slammers for a game with "Mercenaries" and never managed to make things fit together that well. The technological assumptions between the two are just too great. You can use the Slammers as an inspiration for a merc unit with "Traveller" technology, but you aren't going to have anything that resembles the Slammers without actual Slammers technology.
As with FTL communications and FTL travel, Mongoose didn't bother develop any of the signature Slammers' technology for their source book. Instead, they shoehorned the Slammers into "Traveller" and that's one big reason why the book is such a disappointment.
What about grav tanks for the panzers? Up against the tech level-7 balkanized farm boys of Ruie they would be pretty ominous unless the opfor hired Aramis' Azzkickers.
Grav tanks will make mincemeat out of any traditional forces TL 7 can whip up, but traditional forces aren't the only game in town.