85 K5 Charging issues

Hey everyone

I really hope someone can give me some help on this

I have a 85 K5 blazer with a 350 bored 30 over from a 81 corvette. I recently did a rebuild to the motor (alu intake, port and polished heads, and a 472 lift cam)

I installed 2 electric fans that I got from a mid 90s EURO and have it wired on the switch. I rebuilt the Alternator last night and it ran great, but now it wont start unless it sits for around 5 hours.

I have charge going from the alt to the batt, and also to the motor. My battery seems to climb in voltage when a voltmeter is placed on it. Around 16 volts and slowly climbs to 19-20volts.

I have re wired the dash due to lighting issues and everything is clean and done professionally. Any info would greatly help

Thanks

Dibsing