Engine run 1st time for me, now issues

[yoshi]

Finally got my engine (sbc350 1977) started today. I have some issues that I'm not sure if related. 1st off the engine gets hot real quick even with fan running & an external industrial fan used for removing welding fumes in confined spaces. We checked the thermostat, pulled it out while still quite hot & it was open & slowly closed while cooling down. It could be as simple as the radiator blocked. Also there is low vacuum pressure about 5 bar. We believe a new mild cam has been fitted. It's a little lumpier than a standard engine would run. What would cause a low vacuum reading?