You can use bike carbs just like ppl use bike ITB's for custom setups. I am running bike carbs on my 4age in my 86 Corolla. You can find different size jets and rebuild parts online for most bike carbs. Doing the calculations and finding out exactly what size you need for your application is probably the hardest part, and tuning them. I'm sure that an actual kit made for a certain application would flow slightly better than a custom kit made from bike carbs, so response would most likely be better. It is not as easy as it looks though. You can't just slap any set of bike carbs on any engine you want. You have to determine what size throats you need first, then determine the jetting, pick what length you want your runners to be, what grit you want to finish the inside of the runners with, what fuel pressure you will need to run etc. Most bike carbs are also gravity fed gas, which isn't really feasible on most cars. A small electric inline pump with a regulator and gauge set at about 2-5 psi is usually fine though. But, you can save alot of money if you do alot of research.