towing home a 73-87 and got a few questions

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Well I am not new to towing and in the last year have actually pulled hjome two parts trucks. anyways I am trading my 62 wheel horse for a 77 k10. I don't own a car trailer so I was planning on renting one from uhaul as I have done in the past. Thing is they say the K10 is too heavy for ther equipment on the web site. How can this be? IF I enter in 1970 K10 1/2 6 foot bed it says that it is a fine set up. Does the 77 really weigh more then a 1970 K10? I am going 15 miles with the truck but our State (MAss) SUCKS. I mean really they have some crappy laws. I would drive it but you need plates in order to do that and I don't want to get plates for a vehicle I need to work on a bit first. I cannot use a tow strap and mock tow it because again it needs to have plates. Our state will not issue temp tags and if they see you driving with no plate the truck gets a costly ride to a tow yard and the driver gets a big fine. Even if you just purchased it and have insurance..........

So how much does this truck weigh???
I work at a rental shop and the owner said he would let me barrow one of the bob cat trailers but insurance would not cover him if anything happens.

I know your not supposed too but If it weighs what I think it does I was thinking of calling it a 1970 K10 . I had to do this whit my willys 4x4 pick ups because they where too old to be in U hauls comp.

Thanks for any advice or input.
Ian T