carb for slant 6

A 600 cfm carb is too much for a street driver slant, if it is a double pumper, you will be very unhappy. If it is a VS you might barely get away with it, but I wouldn't bet the farm.
It all really depends upon
1) your total budget, for the engine, transmission, rear end, auxiliary systems like brakes, cooling to name a few.
2) your plans - goals for the car, is a daily driver, a full time race car, drags or auto cross?
Figure out what you want to do with the car then see if that carb fits in. If it does not, move it on to someone that can use it.
10-4 thank you buddy