Building a truck for towing 10k pounds

[Road King]

Hi guys, I have had a few hotrods, motorcycles, classic cars and trucks over the years and really enjoy them. Problem is I'm just too busy to use them, one reason is I'm usually hauling or towing something. So I have this idea to build an older truck (67-72) setup for towing larger loads. I often haul a 18' equipment trailer with a Bobcat skid steer or a mini excavator. Trailer weighs 3-4000 lbs and equipment 6-9000 lbs so total load can be close to 12k at times. I haul this around with my newer 1 ton diesel but I'm thinking of trying to mix a little business with pleasure so to speak...?

So my ideas for the truck so far are taking a 67-72 c20, c30, k20, k30 and dropping in a more modern engine and transmission and updating the axle, brake, and suspension. Maybe a Vortec 6.0 with a tow/haul mode tranny. I have also had the idea of taking a newer truck like a 96-2004 and taking the body off and putting an older body on. I feel like going this route I could go with a diesel a little easier.

I want the truck to be safe and handle the load without stressing the truck or me the driver. I want the mechanical side of it to be 10 out of 10 without issues. The cosmetics I'm not as worried about but would like it to be sharp or have that clean, well cared for, original look to it. It also needs to be fairly comfortable and a good driving truck as I would be spending a lot of time and miles in it.

What are your guys's thoughts? Am I crazy? Has anyone done this before? What kind of budget would I need to have this built? Know of anyone in the Madison WI area that would be good at a project like this? Thanks for looking, I'm really looking forward to hearing your ideas.