There are approximately 145 copper pennies in a pound.
There are approximately 181 copper plated zinc pennies in a pound.
There are approximately 168 steel pennies in a pound.
Weights are for NEW, uncirculated 1982 and earlier copper cents, 1982 and later copper placed zinc cents, and 1943 steel cents.
There are of course, more older, thinner, worn pennies in a pound.
Whether you say he had half and half pre '82 and post '82 or even lean a little one way or the other, there would be approximately 260 lbs. in pennies. That is, if the 38,000 number is correct. Honestly, I thought they would weigh much more.