1986 gmc k1500 4x4 350 tbi swap?

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Hey guys I'm new to the forums here, and in need to some guidance on what to do. I picked up a 86 k1500 a few months ago with 4x4 reg. cab long bed, with a carb 305 motor and and th700r4 pushing it. The tranny is in ok condition, from the sound and the feel of the motor the days are numbered on it. So it puts me in the position to start looking for better motor to put in it. The truck was sitting for awhile judging by some of the parts needing to replaced. I would put a carb 350 in the truck with the 700r4 rebuilt but from have one prior to this truck in another truck that motor and the 305 got terrible mpg which we all know gas is going up in price so I was looking for a new fuel induction platform. I began looking at a 5.3 vortec swap with a 4l60e but doing research found that the swap was to heavy for my pockets, so began looking at doing a non oem 350 tbi swap into the truck with a tougher 700 behind it. Now getting to what I need help with, I want to put a 350 tbi with some mods to the motor and convert it over and a cheaper budget. All I rlly want out of it is 300+ hp out of it with atleast 15mpg out of it. I have most info I need for the swap such as a new distributator, new ecu, new wiring harness, fuel rails, exhaust with atleast 1 O2 sensor, for the heads I'm putting vortec heads on it with a eldablock intake manifold with a soup bowl a modified gm tbi with upgraded injectors with a fuel pressure reg. Now that's what I now and want so far I don't no what other parts needed and what to do with my trucks saddle bag tanks. I still want to be able to utilize the 2 stock tank inlets but don't now how to make them work with moving the increased fuel pressure or swap it to a single tank with two inlets. I'm not sure if I want to bore the block and stroke it or just throw a stroke kit in it with good pistons, I want a upgraded cam and parts I like a little chomp to it, I'm thinking to put 35's or 37's tires on it with either 3 or 6 inch. With the unknown motor specs I don't know what gearing to put in the diff. With what I have so far can you with me fill in the blanks any suggestions. Please and thank you.