Remember, a cam in a 273 will act more radical than the same cam in a 340 because of displacement, so I would stay with the standard 340 cam. You might need higher compression for the bigger cams because of the longer duration, ect. I had the 528/284 solid DC cam in my 273 and it sounded wicked, but it ran better when I put the 340 cam in it, much more responsive . That big cam didn't do crap until around 3500rpm.
I used a Comp 282S in my 65 commando short block with 66' 273 heads w/ 360 valves. I used a stock converter and had no problems. Sounded good and ran awesome.
A looser converter would have been a bit better for 1/4 mile but it ran great though.
hey since you already have the adjustable rockers no use going backwards to the sloppy hydraulic valve train [not that it dosen't work] the 273 rockers are supperior, mopar cam 4529346 is real nice 276in 276ex .490 lift 112 lobe seperation real nice cam the only thing is that you cannot get them from mopar anymore but i do have one new in box with the lifters posibly for sale if you are interested all i have now are big blocks. 0/ the 282s has 282in 282ex .495 110lobe seperation the higher lobe will idle slightly better the stock 340 has a 114lsa