Re: 4-bolt cap question
Sounds like it's an original 4 bolt but without the deck stamping it can't really be verified as an L78. Whether it was an original L78 or not is a moot point because it can't be proven and in my opinion the price should reflect. It's just another 396 now.
Since the stamp is gone it can't be a "perfect" restoration. In such case I would buy a cheap 454 and use an internally balanced 4.25” crank and dress it like an L78. Apart from the casting number on the back it will be just as correct as this block without the deck stamp but probably cost less. More power for less money? That's the reason I'm a Chevy guy.
But that wouldn't make it a "correct" restoration either if that's the ultimate goal. I guess that's why I'll never do a "perfect" restoration. The expense of trying to get all the right parts and the pearl-clutching over every little detail is exactly why I love my base model junk.
Sorry about the tangent. I can't help with the caps. I just don't think you should pay L78 money without hard proof that it actually is one.
69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt
76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt