Undersquare was more an issue (back then when conventional wedge heads and optimized valve angles and chamber designs were not well-developed) of favoring bore over stroke so that you could get the biggest possible intake valve in the motor. (all else being equal). Today motors tend to be smaller bores and longer stroke from the factory because torque and part throttle tends to be more important then peak power (as was nearly always the case back then as well). Pontiac's profit money was in loaded Bonnevilles and grand prix that weighed 4200+ pound, that took precedent over getting 10 more horses out of the GTO's 400.
Cylinder heads have come a VERY LONG WAY since then (50 or so years) so although for a given displacement an oversquare motor will tend to make more HP per cube, it's not always a practical consideration when trying to get as many cubes as possible within a given engine block. Bore spacing tends to be much more limited than crank center to deck height....more room to grow UP rather that OUT.
As for an LA, I know of a 501" 4.5" stroke motor that Ron Silva built with Cam specs nearly identical to my 517" low deck Big block.
I build my shortblocks (which tend to ALL be strokers these days) for torque and my heads for horsepower....that philosophy seems to work really well for me as the best of both worlds.
4.25" works really well in the LA with a 6.2" rod and a 1.26" compression height piston. but for maximum horsepower (hp curve, ie, shooting for between peak torque and peak HP RPM band and with the least amount of rapid fall off after peak HP RPM) I would build around the 3.79 stroke and as long a rod as I could get.
