Ive used my PRC-320 on various SOTAs, so long as you can handle the weight then they are fine!
I would suggest that if using radios of this weight, then doing so in a team is best, that way the radio carrier doesnt have to haul anything else - the rest of their kit being distributed between the other team members.
I have a full collection of UK-PRC Clansman radios. The -349 is not of any amateur use (wasnt much military use either!). The -320 is the HF set, the -350 and -351 are the only usable VHF FM sets. The -351 I think is similar to the PRC-77 and very heavy when compared with what modern radios can do! The -350 is a 2W FM set that just manages to cover 6m in 25kHz steps. I ‘might’ take mine up GW/NW-001 Snowdon this coming Thursday!