Does anyone make 1/35 scale figures that depict marines in the back of an LVT-4 getting ready to hit the beach, so far I’ve only found crews for the lvt-4 but that’s as close as I’ve come, or are there any figures that could be modified.

Would the army have used the LVT-4 int the pacific as well, such as at Okinawa?

Depending on the beach they are hitting.....The Italeri figures would be fine for Iwo Jima and or Peleliu beach landings as some marines initially wore the M1941 Field Jackets like their Army brethren. These were quickly removed given the heat of Peleliu, Iwo Jima I think was a bit cooler. Also to note at these landings the gaiters which the trousers are bloused into were worn uniformed contrary to a lot of other marines with trousers not bloused and worn outside the gaiters over the boots in other Island landings. The trousers will need the pockets scraped off for the herring bone twill green look.
For guys standing in the back of the LVT these will be fine...In saying that I believe the May west/ life vest flotation devices may be different for the Marines than the Army boys in the Italeri kit....
I personally have used Masterbox 1:35 US soldiers Overlord 1944 "Move Move Move" set and the US Rangers D-DAY set, Dragon US 29TH Inf. Omaha Beach for Marines at Iwo Jima and Peleliu (with a lot of cutting, scraping pockets off pants..lol) .....but you need to check reference material for correct webbing/ packs used again as there are some variations with kit from Marine - Army.

As previous mentioned the Warriors and Verlinden resin kits are nice but again have a lot of figures with pants not bloused and no M1941 Jackets on....so depending what beach you are hitting or you don't care for detail these are great.

Great reference material/ reading for uniforms...Osprey Campaign 81, Iwo Jima. (M1941 Jackets and gaiters in a lot of images)

Helmet for my pillow...by Robert Leckie.

With the Old Breed....Eugene Sledge.

The Pacific Mini Series HBO...again historically accurate for uniforms worn at different beaches.

Great art work (detail provided by vets who were there, TWILL SHIRTS and M1941 JACKETS WORN).....Off the Beach!
- With The Old Breed on Peleliu -
a fine art print by Matt Hall

Of course for an LVT-4 you could do something from the crossing the Rhine. British guys standing still are a bit more common? The old Tamiya British patrol set would be a good start.

The US 17th Airborne was also ferried across the Rhine.

The ancient Italeri US Marines were just standing around with a wounded Marine. Replace the heads and they're all right.

At least one diorama back in the day used the Airfix multi-pose Marines for the scene just overlooking the scale difference.

There were also several river crossing in the ETO using US LVTs as well as use, If I recall correctly; Anzio.