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I've got a 49 - 3100. Finally have the funds to get started getting it on the road. Currently it has a 235, four on the floor, and Pat's 3.55 r&p. I'll upgrade to 12 volts, disc brakes, maybe air cushions, and definitely A/C. The 235 runs well, but I'm thinking maybe underpowered. I'd like to run 70, at least 65 and with A/C, I don't know if the 235 is up to the task. I'd really like to keep floor pedal for starter, and I actually use the granny gear on my deer lease. Ive thought about the 302 route but cost and size are very problematic (my research). Any great Chevy I6 that will bolt up and meet my needs?

Is the 235 stock, or has it had some modifications? I have a 235 in mine (not stock) with an overdrive and 3.90 gears, it'll run 80+ all day long. If you're looking for more power in a stock appearance, though, look for a 261 from a 2 ton. Pretty much a direct bolt in, keeping the stock bellhousing and starter.

Completely stock. Where did you find the OD unit? Is the 261 have hydraulic lifters? I prefer not having to adjust, but not a showstopper. Thanks for the reply.

The overdrive I'm using the Borg-Warner R-10, which was a factory option on trucks starting in '55. It's an integral unit with an SM318 3 speed main transmission. With the 3.55 gears you have, an overdrive might put a 235 out of its comfortable rpm range.
If you use a '58-'62 261, a hydraulic cam should be able to be used in that block. They are solids stock, though.
Another thing you might consider is a taller tire. That will also help with getting a bit more speed with less rpm.

A Canadian Pontiac 261 came with Hydraulic lifters originally, if you happen to come up with one of those, or as Bill stated a 1958-62 can easily be converted to hydraulics.

My 261 has the higher compression 848 head, hydraulic lifters and R10 overdrive. Its like Bill said. It will do 80 all day. I like the setup so well, I am keeping it during the frame up resto. Looks stock, has a bit more horsepower, and its all a bolt in situation. No need to break out the welder for anything.

I like the normal newer style driveline, so I got myself a 55 1st series rear end, I think the ratio is 3.90 (its stock so correct me if I am wrong) and the driveshaft out of a 62 suburban. Open driveline just felt better to me. Its a preference thing. My 261 is a 1958 model and I had to order the hydraulic cam, lifters and rods special from my engine shop but they didn't have any problems accommodating.

Thanks for all the info, any idea what the final drive ratio would be with the OD? Dave, with your setup, do you feel like you have the Hp for an AC unit?

From what I've read while researching the A/C subject, the modern rotary compressors don't take as much power to run as the older compressors did. I have a 0.60 over 59 model 261 in my truck, has a small cam, headers w/dual exhuast, 390 rear and will run 70/75 all day long and not break a swet. So I would have no hesitation about installing A/C If I had the extra $$$.

Lots of people with 235/261 engines have AC. I plan on doing that on my current restoration. I have never done it before, but I feel the engine can do it easily.

I remember reading somewhere( one of the rpm calc) that the B/W od that longbox has ,when used with the 3.90 rear and I think it was 28 inch tall tire was somewhere around 2.73 final drive ratio.

the OD gives a 0.7 reduction, so with a 3.90 rear [standard] the 'final' would be 2.73 - the OD equipped trucks originally came with a 4.11 rear, which would give a 2.87 final ratio

Bill