I think these vintage names have the same vibe as Harold nn Hal. All are strong and distinguished.
George - Hal and George are great together.
Frederick - Fred, Freddie would be fine with Hal.
Francis - Frank and Hal - perfect! Even Frankie would work well.
Edward - Ned would be a wonderful nn to go with Hal. Teddy would be cute too!
I would eliminate these names from your list. They either don't have the depth that Harold has in abundance or they begin with the same initial.
I vote Frederick, though I prefer the Frederic spelling.
Other names that would work are George and Barett, I think, but less so.
I like Edward. I think Ned and Hal or Ted and Hal would sound really good together. I like the formal name/ nickname like with Harold nn Hal again.
My second favorite is Frederick.
I also like Kurt, Hugh, and Francis. I dislike Tomberlin and Holt. I would like Thomas.
George is my favorite! I also think Frederic and Hugh would work really well.