I built a 400 over the winter for my 68. And of course it wants to run 225 in 80deg weather..

My question is- will plugging the passenger side head and water pump housing that leads to the heater core affect coolant flow or higher temps?

I have done all the usual.
stamped impeller water pump
divider plate mod
180 stat
Running a aluminum rad with 2000cfm elect/fan with shroud. complete build so I know the block is clean.
Timing is set at 14deg intial with adjustable vac advance it come all in at 28deg total at 2000 rpm