You can get regular plates and pay the going rate for PA tags and most likely commercial insurance. Then you could apply for the Classic tags.
In order to qualify for Classic tags, the vehicle must look like it did when it came from the manufacture. Yes, like new with an original factory type paint scheme. No dents, rust or modifications that were not offered by the manufacture.
In order to get PA Classic tags you will be required to send 4 photographs to PennDOT with the proper paperwork and fees to get your title branded for Classic. The photos are front, rear, left and right sides. If it doesn't look like it's new, chances are your application will be rejected.
Once you obtain the Classic tags, you can investigate insurance coverage with an insurance provider of your choice for rates and possible conditions and limitations.
I would recommend that you fix up the truck (make it look good) and apply for the Classic tags and see if PennDot says it qualifies. If it doesn't pass, go the more expensive route and get regular tags till you have it ready to try and pass for Classic tags again.
Keep in mind that Classic tags still require you to get the vehicle inspected. 2.5 and 5 ton trucks are required to be inspected every 6 months.
Karl