Problems I see building trucks is that you're competing with the pricing on used trucks. Ppl will usually go for the low dollar and try to save. Not everyone out there is selling junk that needs a ton of rebuilding. There are DEF good deals to be had out there. Like anything, it's VERY difficult to buy things new, modify to what YOU see as the 'best' or the 'right' parts/way etc... and then sell it with a profit margin that takes into account your labor etc... You put on XYZ tires and XYZ engine... The purchaser wants only ABC tires and ABC engine. Then the profits... A brand new kit costs 400, then you put in the engine for 200, then 200 in parts... Already, there is a guy who put that same money in for MOST of what you installed and he is selling it for 600. Even tho he used it for 6 months, he used it and maintained it like he loved it... Even tho it got used, he planned on keeping it for years... Problem is, HE just found out his girlfriend is pregnant and he needs to sell his toys for Dr. Appointments etc...
See, there are a MILLION stories like this... It happens ALL the time! There are too many deals out there for you to be able to compete with on any level. If anything, you may be able to establish yourself as a builder... Even then, you would be competing with hobby shops who WILL build to suit their customers and they are buying their parts at hobby shop (wholesale) prices. Their mark up is included in the sale price before they turn the first screw. They tack on another $100 to build the kit per order from their customer and they have just made a KILLER profit in parts and labor... Are you gonna tie up $800 in kit and parts for $100 in profit that may or may not sell in a week, month or year??? There are better ways to make a buck and they are Def more consistently gonna turn that dollar! Spend the $800 on a lawnmower! (i don't mean that as an insult either!) you're more likely to make that $100 back doing lawns for your neighbors!
I'm sorry. I don't mean to shoot down your ideas... I just see the holes in the plan and is rather tell you why I don't think it will work rather than hearing you failed. As with all members here, I wish everyone the best of luck.