fooling my small block

I haven brushed anyone off I dont think. Least I didnt try to.. sorry if you took it looked that way I get a lot of "I just want the sound.." type questions. IMO, that's like shopping for a new car by color alone...lol. So if i offended, I apologize for that.
A short story/salespitch: I drove a '74 Cuda for a few years. It was a stick, 3.23 SG, and had a stock ring and bearinged '68 340, stock X heads, stock '71 intake and Thermoquad carb, small tube headers, and 175 shot on it. Well, being young and stupid, I got stuck, ran cheap gas, and blew 1/2 the ringlands off a piston. So I pulled it, replaced the shortblock with a stock '74 318 (guess from where??), stuck the same cam and top end and NOS on it, and ran it. The car went 13.50s off the spray with the 340 on Dunlop radials. 13.60s with the 318. It was so good in fact, that only a few friends who noticed the color change on the block ever knew I had hurt the 340. The cam was the 268H Comp Hi Energy. 218°@.050, 268° advertised, .454 lift. It had a noticable idle in the 318. It was not soft just off idle tho. I drove this car everywhere, and didnt have to slip the clutch to get moving. My point being, that cam is an old school single pattern with 110°.
Huges can do whatever they want. The latest grinds I've heard about make me wonder what they're doing. But that's them. They've forgotten more than I know now...lol. I'll stick to what I know. The best way for any short stroke engine to get air in, is to draw it in until inertia (rpms) helps it out. It cant draw much air in hard at lower rpms if the exh valve is open at the same time. Now, maybe Hughes uses an incredibly fast closing ramp on the exh valve's lobe. To minimize the time they both are open, but still have decent duration under the curve. That might explain thier heavier than what most reccomend for valve springs too. It's hard to control a valve and harmonics when it slams shut that fast. Who knows.
From what you've said, what's holding you back is the valve guide height (not seals). If these are normal X/J/O/915 LA heads, you have more room than you think to go with lift and 1.5 rockers... Guys throw in .484 and .509 lift cams on stock height guides with no issues all the time. You will need matching springs of course, but they will have to be changed anyway. I think it's mid 80s LAs that use a full rubber positive type seal. Install them with the springs. That way you're not squishing the large umbrella seals all the time. It's the Magnum heads, and 360 LA w/exh valve rotators are the ones that can't take a ton of lift in stock form.
If money is the object, give Engle Cams a call. They ground me a custom solid with lifters for $189. They also used to grind Hughe's cams, and have a keen awareness of spring pressures and break in issues. (310)450-0806. They have some very nice looking lobes for mopars, and can also give you a great price. Your going to spend one way or another. Might as well get more of what you want.

"Theoretically a tight LSA should balance that loss of velocity within reasonable parameters, right?"

Right. However, on large port, small stroke, low compression engines, that parameter rpm wise is about 2800-3000 rpm depending on a bunch of other factors.