So lining the gears up dot to dot would get you pretty close, nothing like being off a tooth. Off a tooth, something would likely hit or tun far worse. Barry was referring to a very late ICL due to tolerance stack, errors in machining, or even accidentally picking the wrong slot in a multi-key bottom gear.
One thing you may want to do is check TDC with a piston stop to see if your balancer swap has your timing off. If you haven't done that before, you screw a stop into a spark plug hole, by hand, turn the motor until it hits, mark the balancer at the timing pointer, then turn the motor the other way until it hits again, mark the balancer. TDC is the exact middle between those two points. If you are off, timing could be off and make it pretty snoozy
Didn't realize you had an RPM at first, but since you do, assuming timing curve is right, I say cam change next. However, I agree with Barry that low vacuum is odd with a 268H and a 428. Maybe try a second gauge, then advance the timing 4-6 degrees and see if it changes (not saying to run it that way, but would be interesting at idle)
As far as the XE274H and current springs, I would expect them to work fine, but, as I told 427HISS, you should really check at least one. You are going from .494 lift to .565 My hunch is you'd have an open pressure increase of about 25 lbs, but you need to check, to include checking for coil bind and valve clearance and maybe use a +.050 keeper during cam break in. I would recommend degreeing that one though if it's an option
I do not think you need to change to adjustable valvetrain for a 274H, in fact, in most cases, I'd recommend against it because stock rockers work so well.
