Chainmaker, what I meant in my earlier comment regarding your proposed changes affecting the handling is 3 basic issues -1) insuring that the front steering geometry is correct for Ackerman angle is imperative, and getting zero point suspension lean on each kingpin. 2) Lengthening the wheelbase will impact your turning radius drastically, and wider front rims/tires will as well, as you have to consider the arc the front wheels will swing through in turns - typically the wider the tire for a given wheelbase width, the less the allowable angle of turn (you definitely do NOT want a spinning tire rubbing against the outsides of your thighs), and 3) the seating height on the Warrior looks to be 6 inches or less - high centering the main frame gets more likely as it gets longer for a given height above the pavement.
Along with those concerns, the longer the moment arm of the main frame tube, the greater the likelihood of rear wheel scrub when cornering, as well as torsional deflection of the dropout subframe. Going to bigger/heavier tubing is a good idea with your proposed changes. With the tadpole type recumbents, a CoG that is well forward (but behind the front steering axle plane) is important, because under braking forces the bike will want to nosedive - it is quite possible to lift the rear wheel off the ground. With the lengthened frame and the very large/heavy rear wheel, the CoG will shift backward. Which means that it may well be advisable to go with a disc brake on the rear of your design, but make sure that your force balance is at least 60/40 front/rear brakes - the front bakes must be primary and they MUST be balanced.
I like what you are proposing to do, but please do think through each changes impact on the bikes useability carefully. Think about your chain runs, and what lengthening them and/or changing frame member angles will do to them. In addition, with that big a tire, how are you going to affect power transfer? Are you going to bring the two power systems (pedal and engine) together at a mid-drive unit before final transfer to the rear wheel?
Most useful to me in design questions is a good 3D model - I use Google SketchUp a LOT - and then I try to put myself in the seat, mentally. I spend a good bit of time working out what forces will be experienced, in what directions, in use. Better to work out as many bugs as possible before investing effort in fabrication than in changing things afterward.
