I think you want a mixture of Higgins Boats (LCVP) and LCPLs. Both were used at Guadalcanal and photos of the LCPLs definitely show them in navy grey. For what it’s worth many of these boats were manned by the USCG.
LVTs were LVT-1s, their first outing. Un-armoured and unarmed, though the marines did add an assortment of weapons apparently. Still viewed principally as a logistics vehicle at the time I think.
Guadalcanal, Saipan? Come on you really want LVT-4s for Tarakan and Balikpapan.

The OTP stuff is good, albeit it’s a long wait. Just a pity the roofs don’t quite fit on some of their buildings. The vehicles in resin are top notch though.