It's a store brand model that uses the Premier 125cc model as its set-up and is a 73-74 model, so that makes the G3 carby spot on!!! Store brand mowers that have a model name after the words "Store Brand" don't always use the model name that the parts reference guide gives, so just because V149 says "Store Brand Premier 125cc" doesn't mean that the words "Premier" will be on the mower any where.
(SPECULATION) It's my understanding that the Store branded models have a Victa model name with them, but it's only the model type that the store has chosen their commission of mowers to look like and is in no way what the actual model is, the model is what ever the store commissioning the order of mowers decides to go with. Also I believe that the model name is in the quick parts reference guides to make life easier on the guys who have to do repairs, if they know that it's actually a "Premier" then it's much easier on them in knowing what they are working on and the right parts, but it's not a Premier it's whatever the store decides its name to be.
The year of the engine build will be determined by the serial number on the case. I have no information for you about the barrel question tho, sorry.
Can you post some pictures please? I'd love to see it and a picture of the V149 code would be awesome too please! I collect as many pictures and real ones I can find.