expect $1500 plus in parts to retro a old blower plus carbs, i do alot of these. Yes if your street driving i would definately buy a new idler bracket and idler. To make things safe and reliable i would buy a new snout
sbc street blower intake $400
Snout $350
Idler $250
Blower belt $100
3-4 8mm pulleys $200
Dual carb adapter for blower $150
New good bearing and seals $125