Hi Mike, welcome to the Stovebolt!
I have a '55 1st GMC Suburban.
Mine has a 270 with the original type 4-speed, disk brakes on the stock front axle and a later rear axle with 3.08 gears on the rear. It isn't lowered except I'm running lower profile tires on 15 inch wheels. I have power leather bucket seats from a Honda Accord.
Its very drivable, stops great, handles like a SUV, will run the freeway at 70+, and accelerates well enough to stay with traffic, and the seating is comfortable.
Those are somewhat subjective measures, and you might want to change some of my choices.
I'd like power steering when I'm in a parking lot, otherwise it would not change driving this truck at all.
I've considered swapping the original granny gear 4-speed for a Saginaw 4-speed, or alternatively changing both the transmission and the rear axle to use a T-5 with overdrive.
While sometimes its hard not to trip over 235's, finding a 270 is not hard. Finding a 302 is a little more challenging, but they are out there.
If you are serious about running a GMC inline you should check out the forums at OldGMCTrucks.com. You'll find more information about these motors and possibly even find one for sale.
