Long ago, a Cathay Pacific pilot with whom I sailed in Hong Kong brought a replacement mast up from Australia in a 707. He said it took a bit of effort to feed it in the rear door, but once inside it neatly up the aisle and passengers stepped over it quite easily. Can you imagine trying that today?
Many years ago when I rowed competetively I was told that a load on the roof must not extend in front of the car and a max of 6 ft behind it, unless it was a boat propelled solely by oars when you were allowed 10 ft overhang front and rear. You had to have a flag front and rear and lights at night. A club member transported his sculling boat (27 ft long) on the roof of a mini routinely. He got stopped by the police for an unsafe load, as he was a solicitor he won the argument.
I looked into the overhang rules recently as I wanted to transport a 10.2m roller reefing foil etc. (It turned out my sub-5m long car wouldn't quite allow this.)
The limits are -
2m forward of the vehicle; and
2m to the rear, or 3.05m to the rear if you fit specific design warning triangles.
At the front, and with a max 2m rear overhang, you just need something to make its presence/extent visible.
There are much extended allowances for (registered?) racing rowing boats.
If you exceed those dimensions you must get the permission of the police, which I imagine will lead to a paid police escort being required.
There was an interesting article in PBO or YM some years ago by someone who'd transported a rather large mast by car, IIRC UK to S of France, paying great attention to the differing(?) rules in the two countries. He build a stout pyramid-shaped wooden frame, point upwards, mounted on top of two roof bars on the car, and then another similar frame on a large trailer. The mast was suspended on ropes from those two frames. These ropes accommodated the changing distance between the car and the trailer as it went round bends and corners, but other ropes prevented the mast swinging too far forward or back, and kept it fixed laterally under the frames to stop it swinging into them. The mast was transported successfully, and didn't attract the attentions of the police.
Once moved a hefty wooden mast about a mile by "borrowing" a squad of 30 trainees during their daily PT session. Then reversed the process a couple of weeks later after it had been stripped, revarnished and new wooden spreaders made.
Friend repaired his two wooden masts in my w/shop down in Portugal. So how to get them to the dock at 10km away? Main was 50ft...
Strapped a trailer to the middle, screwed a hitch to the foot and set off at first light Sun morning, as I really didn't want to discuss this with the police. Side roads with a lead car and chase car. Lead car looked carefully at the two main junctions, then signaled the 'load' to go. Towing into Portimão was not on, so we put them in the river upstream and towed them to the dock. I don't the 'indevisable' load would have worked as a defence
As a guide, the GNR would 'do' you for more than a 10cm overhang on the car.
Preferred method for short distances is to balance it on a barrow and get some mates to help push it.
There are very few rules about the construction and use of hand carts, compared to motor vehicles.