A couple of things to think about.  1) does your current motor turn clockwise or counter clockwise?  I bought what seemed like a good deal for a motor to use on my bandsaw only to find out it turned the wrong way and wasn't reversible.  I didn't realize it until I had a few people over in my shop to show off my new upgrade.  I instantly blamed one of them who had advised me on the upgrade, you may not be so lucky.  2)will it mount on your lathe?  And will you be able to use your lathe the way you want to i.e. turn your headstock is the big one once it is mounted?  3) If you are going to upgrade why not go for the gusto and go with a true variable speed setup?  I did this on the advice of a friend to my first HF Lathe when I got to a point of needing a better lathe but couldn't afford a really good lathe.  I bought a 1.5 hp dc motor and with reversible controller on ebay for $325 delivered It was wired and ready to mount and plug in.  I had to made a different mounting arangements so i could turn the head stock and match up with the other pulley but that was simply done with some scratch BB plywood.  I later added a piece of sheet steel to it to add rigidity.  If I hadn't cracked the head stock out of carelessness I would still be using the thing.  (Always remember to tighten down your head stock when you rotate it, but don't over tighten and especially don't do it 6ft of pipe over the end of your torque wrench when you are trying to loosen stuck nuts off the back side also remeber which way nuts titghten and loosen when you are looking at it from the wrong direction).

you can do 8 to 12 with the motor you have now you just have to go slow, I have made 15" on the outboard with the stock motor.  1hp will do you fine as well, if it is the hf 1hp motor you might need to make a space for the mounting plate,I can't remember for sure, but I think someone told me it got in the way when turning the head stock.  This is really a simple task just get a piece of 3/4" ply mount it on the stock plate and then another mouted to the bottom of the motor and mount the 2 together with the right amount of offset with the head turned 90 degrees  The only other change you would need to make would be the size of the belt to compensate for the extra distance.  Another thing to considder when making the bigger bowls is speed.   Because of the way the 34706 is setup (as is the jet 1236) you are not getting the lowest possible speed you can but rather getting something like 700 rpm.  That still is technically in the safe zone for turning but it would be better if you could go slower.  Since your not waiting for a dc setup (though i suggest you look locally on ebay first you might just get lucky), you can also get a reeves drive pulley online to change the ratio and slow it down.

modifying the reeves drive requires a little more than just changing the pulley from what i understand .  There is a spring on the shaft itself that helps move or rather hinders the spee changer movement which needs to be trimmed and while your at it you should fix the speed control handle so it moves into the slowest speed.  there is an online turtorial for that.  you will also have to remove the sheet metal cover from the lathe and build another one that will give clearance for the bigger spindle pulley.  A simple plywood cover should be enough to keep the dust and shavings out of it in lue of the metal one.  Another thought if you are handy with tools since you would already have the shaft stripped down now would be a good time to put new/heavier bearings in.

As far as controllers go they don't have to cost that much.  look around and you can get them for $25 to $50.  However the best deal if you aren't electricly inclined is to get one that is already wired and ready to plug and attach to the motor.   The one I got came ready to mount and plug in.  It took me all of 90 minutes from the time the UPS driver dropped it at my door to start turning and that included a trip to ace hardware for some mounting bolts