I’ve done that pig roast thing a few times (actually some Cubans did the hot work) and it is very simple. All done in the Caribbean with Caribbean technology – cutlasses (machetes), optimism, rum and loud argument.
The fire is in half an oil drum (semi-circular section), spit is rebar (longer than you think), supports are forked sticks driven into the ground. Slow is the key and it is surprising how far above from the fire that means. Keep the spit turning continuously but slowly. Impossible to give a cooking time but it won’t be less than 4 hours and could go to 8
Lots of different secret recipes for rubbing, basting and marinades.
Pre-plan somewhere to dismember the beast. YOU CANNOT DO THIS ON THE SPIT AND YOU CAN’T WING IT. I use a trestle table covered with baking foil. Once you start cutting it can get pretty big on you.
Use the smallest pig you can(less than the barrel length). Problems seem to arise by the square of the size. However it very easy to underestimate how much pork drunk people can eat.
Easy on a tropical island. Brave effort in UK.