I have no first hand experience with Hughes cams, although I will this winter as I have one going in to my 360. Hughes does have a lot of good mopar experience. I've never had any trouble dealing with them, but I've always know exactly what I need and never hit them up for advice. I've seen plenty of other complaints about them though. I won't say they are wrong about the roller lifters, but they aren't far off either. The performance benefit to them and roller rockers in a mild street build is very negligible. Keep in mind the factory did it for emissions and mileage benefits. Adding these items to an engine may increase its efficiency .1%, so for you the gain is practically nothing. For the factory that has to meet mileage and emissions specs as a corporation, a .1% gain over a million engines is a huge gain. Similarly, at high rpm or maximum output, they show greater percentage of gains over stock. Ultimately, power is about efficiency and adding these parts will net an improvement, but the gain for the cost in what your doing will be low and you can gain more effcicieny in other areas for less money. Like them or not, the fact is emmission requirements are what have driven the new engine designs and their improved levels of efficiency.
I've never used Comps calculators. I used to have a Desktop Dyno program but lost it when I upgraded my system because new computers don't operate of DOS like the older ones, so my program was incompatible. What I have noticed about using it, is that you have to be very careful about the inputs as they can create some overly optimistic results. If you are unfamiliar with engine builds and strictly go by the programs, they can lead you down some less than satisfactory paths. They also don't tend to have a big red marker saying that cylinder pressure is a key goal to achieve. It is usually buried in some data points somewhere so it is not easy to understand the impacts change may have on the squeeze. Most calculators tend to put optimal horsepower first and foremost. I'll admit high HP numbers are sexy, but ultimately power is all about torque and the more torque you have across a broader range, the better the engine will perform and the higher the power numbers rise.
Despite their huge production volume, 318s have never been a "go to" set up for performance. So build info on them is definetly lacking and the first response from most people is to dump it for a 360. Since you want to keep it, I guess I have a few questions for you. The two biggest of whats the goal and what the budget? Budget can include time as you mentioned earlier. Goal, obviously more power, but if it is simply the desire to burn rubber, you may not want to mess with the engine at all, or at least get it back to a previous power level. I ask because if that is important, changing the engine may be a waste of effort compared to putting in a higher rear end gear and an overdrive transmission. Same with the torque converter. It will hit the tires harder to make them spin, but stall is created by removing efficiency and the higher stall may leave you even more disappointed. Similarly, stall is created by torque, so a low torque engine with a high stall may be a bigger pig tham a regular stall converter with a high torque engine.
Like CP said, it is putting together a good combo. It sounds like you have good heads, and you cam isn't awful with the right cylinder pressure, so now you need to match up the rest of the combo. You definetly need help in the compression department. The 390 kit will produce increases in moving air and put more squeez on the air you take in. I guess you will need to decide if you want to spend the rebuild money and time to go there. Even if you keep the stock crank and rods and only replace pistons, you are still looking at a tear down and machine work. IMO, a 390 with the 360 heads and your cam should be a decent increase in power.