Hi,
There are many itineraries travelling Cambodia, Vietnam, Laos and Thailand within 2 months. I suggest you here one of the suitable tour.
– 22 days, insight Indochina-Vietnam-Cambodia-Thailand-Myanmar trip:
This amazing tour combines all four of the Indochina nations is the remarkable contrasts of culture, cuisine, scenery and atmosphere that unfold as your journey progresses. We’ll go through all of the most famous destinations in each nation. Hanoi, Sapa, Halong,Hue, Danang, Hoian,Saigon in Vietnam, Mekong, Siemriep, Phnompenh in Cambodia, Bangkok, Chiengmai in Thailand and Yangon Bagan in Malaysia. 
For the detail. you can check here http://www.discoveryindochina.com/tour/22-days-insight-indochina-vietnam-cambodia-thailand-myanmar-trip
– 22 days: Vietnam, Lao and Cambodia:
Itineraries : 22 days / 21 night
Activities : Chiengrai, Pakpeng, Luangprabang, Hanoi, Halong, Sapa, Hue, Hoian,Nhatrang, Dalat, Saigon, Mekong,Phnompenh, Siemriep
For the detail: http://www.discoveryindochina.com/tour/22-days-indochina-adventures