As several have mentioned being able to tune and adjust is real important with this kind of application and although the single line carbs can be tuned to work they generally take more time and may have to be modified in the end.

Other issues that haven't ben mentioned in regards to a single line carburetor is their orientation with them being front to back as opposed to sitting sideways. With the space constraints most will not have secondary metering blocks where you can change the jetting but also this means the carbs have to come off anytime changes are made.

We prefer to use a sideways mounted carburetor for tunnel ram applications with front and rear metering blocks. With them being mounted sideways jet changes are as simple as pulling the exposed bowls off. Also going to the center hung bowls allows you to use angle cut floats which will help in float and needle seat control depending on how hard the car launches.A carburetor that is specifically calibrated for tunnel ram use will also have the transfer slots restricted as well so there is not an excess of fuel as both carburetors sweep the slot.

Up until recently we only offered tunnel ram calibrated carburetors in our more expensive Race Demon series but with a lot of guys going to milder applications and tunnel rams we now make them in the mighty series as well which is good up to .260@ .050 on the cam duration.

Not really enough information posted to make a definite recommendation on size but generically it would fall somewhere in the 575-650 range and there could be more then one size that would work depending on which area is most important to you.