Cyclocross - IRO Rob Roy setup (noob)

I have an IRO Rob Roy that I got a few years ago to train on. Well that went by and I haven't ridden much in the last couple of years. I also moved to the country and have an endless amount of dirt and paved roads to ride on. I will be mostly on dirt roads for now. I have been riding my old Giant mb but the suspension has way too much bounce and I wanted to go back hardtail. I had never considered cross til I decided I wanted a rigid 29er and found out about this. The RR is setup for road use and I want to change that. My current setup is:

46/17 (way too high for the dirt roads)
170 IRO cranks
700*28c road tires
36 spoke wheels (I am still and will always be a clyde, but hope to lessen that with the new ride)
drop down bars

Can I get the gearing down to close to 2:1 (or whatever is best)?
I want the biggest tire I can put on (IRO says 35)

I guess tires and gearing are my biggest concern. I don't have a LBS that can help so it's up to me. I think I could tackle the gearing with the right tools, but don't know where or what to get. I have searched for a couple of days and decided to just ask. Sorry for the total noob questions, but I really want to do it right the first time. Thanks for the help fellas.

Well since IRO has been closed for inventory for a week or two I still haven't made any progress. I think I will just use 35 tires. Leave the cranks alone, but I called a lbs for a new chainring, but I don't know the dimensions for the chainring. I guess it's the ID I need. It has 5 bolts. Does anyone know the inner diameter for an IRO crankset. I guess a Surly would be a good choice. I figure I will get a 34 and a 36 or 38 to play with the gearing.

IRO cranks are 130mm bcd.

A 35 is as big as you'll be able to go in back for sure. I'm running a carbon fork & use a Bontrager 1.8 tire up front. I currently use a Specialized Captain CX tire (34mm) in back.

FWIW, I currently run 42x18 & it's a hair too easy on ashpalt. I like it on limestone & singletrack trails for the most part.

Thanks for the help guys. I'll give it a try.

Thanks for the help guys. I'll give it a try.

Best option is to try it out and base your money spending on actual experience rather than speculation. Otherwise you'll get bitten with the money-spending-waterfall, whilst fun will cost you more in the long run. I am learning this lesson the hard way ;).

i run 42x20, and I think its perfect for a rolling offroad course. I think 40-44 are the best chainring choices because you can make it a road setup easily. On my flip-flop hub, I have 42x20 free/42x17 fixed, and it works with the same chain.