Just got a 70 GMC 1500

[94gmc454]

I just purchased a decent 1970 GMC 1500 Custom pickup and have several questions for all of you who are in the know. First, the seller tried to tell me that it had a 350, but I'm thinking it might be a 307. How can I tell? I'm not convinced that the engine is original. It has a greenish blue intake with a 2 bbl Rochester carb on it. The valve covers are orange. The block is stamped on the front pad with the following: K11 21 DAF Then under those digits are the following: 48H164537 There is a fair amount of "cobbing" with the wiring in the engine compartment as well as under the dash. The original heater switch has been bypassed with a toggle switch under the dash that has a hot wire directly from the battery. I have a buddy who is planning to repaint the whole truck for me in the original blue/white two-tone and have already purchased a ton of parts to replace the missing/broken/worn ones on the truck. I'm thinking that maybe I should replace the wiring harnesses as well, including the fuse block, which has some rust and corrosion on it. Any suggestions where I can get decent used harnesses or new ones that won't cost as much as I paid for the truck? I appreciate all the help I can get, thanks!