Not necessarily a 61-66 truck problem, but people here seem pretty knowledgeable and may be it will help someone with a transplant...
My 87 F150 w/300 (EFI, Serpentine belt, A/C, smog pump, power steering) is having a bad belt squeal issue. I recently did some power steering work, bled the system, and put a new Motorcraft idler pulley and Motorcraft belt on. By process of elimination (the 'ol WD-40 spray and see what stops squealing) I've determined the new idler pulley is the culprit. I spray it and the engine runs nice and quiet.
Is the pulley something I can grease? Maybe I got a defective one or maybe the "new" ones aren't quite right? Anyone out there run into this issue and have some guidance?

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'63 F100 223 3OT
'87 F150 XLT Lariat 300 3spdOD
'03 CVPI

That is typical of a bad tensioner or press on power steering pulley that has creeped it's way closer to the pump. Get an eye shot of all of your pulleys. Look on the passenger side and line up your alternator with your water pump and crank pulley. The face of all of your pulleys should square up. Check your new idler offset against your old one. If the old one had a spacer/washer built onto the pulley make sure the new one does to.

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Chris

Thanks for the reply chris401. It looked like the belt was rubbing on the edge of the pulley ridge. The offset on this idler pulley appears to be different font and back. I flipped the pulley around and it freed up some space.

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'63 F100 223 3OT
'87 F150 XLT Lariat 300 3spdOD
'03 CVPI

Jumped the gun in my response. Finally had time to run the truck. Long story short, putting the old belt on fixed the squeal. I’m assuming I must’ve ruined the new belt with either A) the WD-40 or B) ATF fluid from bleeding the power steering

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'63 F100 223 3OT
'87 F150 XLT Lariat 300 3spdOD
'03 CVPI