My comments aren't met as negative ones. But, you're not going to get more power from a 6.2 diesel as compared to a 350 gas. It's also going to be more difficult to work on an maintain unless you've got some diesel experience and tools. I was a diesel mechanic in a truck and tractor shop when GM came out with their first diesels - in the mid 70s with the Oldsmobile based 350 diesels, and later - first year 82 when the new 6.2 came out designed by Detroit Diesel Co. for GM. We wound up doing service work for a local Chevy dealer -because at the time their own mechanics were not experienced with diesels.
A typical stock gas 350 will have around 200 HP (4000 RPM) and 300 lbs torque (2400 RPM). A 305 gas around 170 horse and 260 lbs. of torque. A 6.2 diesel in naturally aspirated form (no turbo) has around 130 horse at 3600 RPM and 240 ft. lbs. of torque at 2000 RPM. Put a turbo on the 6.2 and horse will be upped to about 190 if you do it safely. The 6.2 has a higher-compression ratio than later engines meant for turborcharging - so boost needs to be limited to 10 PSI - unless you install lower-compression pistons.
A 6.2 diesel will be comparible to a 305 gas in overall power and pulling - but the diesel will be more consistent and power throughout the RPM range. Fuel mileage will average around 20 MPG plus on the highway if the RPMs are kept under 2000 RPM. Average daily driving more like 16 MPG.
The diesel, though, will run a feel different than a gas engine. And, if cared for will last longer. I own many and have driven them for years - with a lot of trailer pulling. The main caution I'll mention is cylinder head temps. If you do a lot of hard low-RPM pulling - mudbogging, whatever - the heads can get very hot and crack - unlike a gas engine. That being said, one of my tow vehicles made it over 500,000 miles before the crank blew to pieces and two main-bearing webs pulled out of the block.
