However it may be...the Firebird, for all intents, without the nomenclature to make it an HO, is not worth any more than if the car was a 400 without it's original engine.
As was stated prior, this isn't a 1 of 7, 1 of 100, 1 of 300...it is a 1 of 1600 +/-. What IS driving the price is simple...it is a decent convertible with a non numbers 350-400 with a decent interior. Agreed that a 400 4 speed vert is a rarity that I would say may have numbered in the 40-80 arena, but it was an option that added a paltry 10 HP (advertised) and again, not in the realm of a true powerplant upgrade as say a 442, W-30, LS6-7. An instance...if a Hemi Cuda vert had the same 426 engine with 4 speed...and 2 engines were available, and the higher output engine was missing, the car would command much more. Why? The engine series alone is what made the difference...Here with the HO 400, there was not much fanfare or performance per se. The 400 HO was not a 426 Hemi...nor was it an LS7 454...or a 428 Cobra Jet.
Now if this HO was a RAI or II, then you would be picking an apple from the same tree.
There are several examples Firebirds exhibiting most of the same criteria for this price.
Yet, the true kicker is the fact it is a 4 speed POWER top vert with a body broadcast sheet...that is what truly is pushing the price. Now add rally gauges, hood tach, console, clock, with deluxe interior...and it is a very nice package, notwithstanding, it appears to be solid underneath and that for all intents, is the driving factor...and not the "HO" appeal. One can not simply find a 400 4 speed vert with a power top in decent condition...the missing "HO" factor is a non appreciable bonus to sell the car, not specifically value per say.
Any potential bidder with some knowledge would understand that finding a WQ block is nearly impossible, then to locate a 8271 carb, 449 distributor and then...the manifolds, well, you'd still have a non original HO worth maybe...10-15% more than a 400 and 40% less than a true numbers matching 400 4 speed vert. What would benefit the attempt of an HO "tribute"? Having all of the missing HO parts and subsequent block...dated within a 4 to 6 week period.
So...in closing, albeit an HO, the addition of a non original motor would essentially be deemed a clone..
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.