Help with a 58 300GH Hydra Matic retrofit

[wamantqs]

Guys or Gals, I'm looking to replace my original 4 on the floor with a 300 GH HydraMatic (this is what is spec'd as original for this model). First problem; finding one to retro into my 58 GMC 150. My real question is; I am very new to the world and grew up a Ford guy; please don't chuck anything at me. I've absolutely fallen in love with the 55-57 & 58/59 Chevy/GMC version trucks. The style and lines are incredible. I just found my baby and am slowly making a few basic changes as my wife wants to enjoy driving it also. I'm going to foster her "want" because it's a surprise that she enjoys the truck so much. I need help finding good places to find NOS and used parts for the truck; can someone point me in a direction that I might find a useable 300GH HydraMatic that I can drop into this puppy? Any help is certainly appreciated. Thanks, Mike P.S. - If any of you thinks I'm making a mistake in taking out the 4 speed, please do not hesitate to give me your opinion. I'm always up for well intentioned criticism.