This is what I'd do if I just HAD
to install a flat tappet cam. Shell out the 40 bucks for these springs, install 'em and run the motor at low r's for the first couple hundred miles. Then, using a spring compressor that works with the heads in place, I'd change out the springs to whatever the cam manufacturer specifies for that particular cam.
Use shop air to hold the valves up on their seats, or feed a length of clothesline rope through the spark plug hole and jam the piston up against the rope to keep the valves on their seats while you change out the springs. Put the light springs in a bucket and label it "Camshaft break-in springs".
Comp Cams 979-16 Valve Springs 1.250" Outer
80 lbs on-seat, 200 lbs at 0.500" lift.
If in doubt, re-read this article. It was written by those of us who have been there, done that many times.
Bottom line Bubba, if you try to break in the cam with 300+ lb springs, you'll be doing it a second time not so far down the road. Suit yourself.