Engine Swap in 1994 k1500

I've got a 1994 Silverado 4x4 (1500), with the 4.3L engine.
The truck has 33"x12.5" tires on it.
I just had the stock 3.08 gears upgraded to 4.10.
The truck does drive better, and the transmission behaves better with the new gears, but I'm really feel that the 4.3L is a bit underpowered for a full size truck with a 3" body lift and big tires. Pushing that brick through the air on the freeway seems to be asking an awful lot of it.
It can maintain 60-65MPH pretty well and the transmission behaves normally (the TC locks up in OD as it is supposed to, and stays put), but 70+ begins to introduce downshifting in order to maintain speed as soon as even a slight incline or wind is introduced. I can only assume it's related to increased wind drag, and horsepower needed to overcome it at higher speeds.
I have access to a 1985 Caprice Classic station wagon with a 305 in it. I would prefer to put a 350 in the truck, but I can get the 305 for free (it would need rebuilt, of course).
What are the differences between the 305 and the 350? (other than the obvious displacement)
What are the differences between the 305 and the 350 when it comes to swapping either one in for the 4.3L?
Does one swap in more seamlessly? Will both mate up with the 4L60E properly? How much retrofitting needs to be done with engine mounts for each?
-NW
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Take my word for it. Get a 350. I have a 93 with a 3" body lift, 31" tires, and a 305. I wish a I had gotten a 350 right about now. The 305 is WAY to doggish for me, but it is decent on gas.
-- ---------------------------------------------------------------- Ed Murray Certified Locksmith My Enthusiast's Website: http://www.crooked-ridez.com

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