These thermostat housings will fix your leak with a gasket seal design.  They feature a beautiful chrome finish and are designed as a universal application for most Chevy and Mopar engines with stock intake manifolds.  This design works with a Mopar thermostat only.  Late model Mopar style thermostats suggested.
 
Neck goes straight up, must use Mopar thermostat
Beautifully chrome plated
Uses gasket for a perfect seal
Center-to-center of mount bolts:  3-1/4"
Neck/hose size:  1-1/2"
Hardware included
Water neck fits:
Chevy Small Block V8
Chevy 90 Degree V6
Late Mopar V8