So i've decided to run the 427, its heavier but I haven't had a bbc and this seems like a good time to jump in both feet
So i took it to the shop today, Dale Maslen Machine in forest grove. Dale is an older guy and says this is the first BBC he's handled in 4 years. He had some stories and pics of his own 427 '69 el camino that he showed me, doesn't have it anymore but it looked sharp and said it launched real hard. He liked the 427's over the 454's due to internal balancing and the quick revs. He pointed out my engine had a steel crank and forged rods. The crank he says looks ground out and doesn't have the cross drilled hole so its probably from a 396. There's plenty of work to get it ready to go and i expect him to find more issues as he dives into it. Pistons are already 30 over, heads will pretty much stay untouched except normal prep work. I wanted him to unshroud the valves but he said there isn't room to work with due to water jackets. I wouldn't mind getting some aluminum heads on there just for weight concerns but unless i can find a smokin deal then I'll stick to what i have so i can splurge in other places.
Transmission-wise I am nixing the t56 idea so i won't have to redo alot of work on the '91 Z28 so i'm left with a 4l60E, a '96 Yukon transmission, or this muncie that came with the engine. Its marked P0A28A (muncie, 1970, january 28th, m20) and the case # reads "392566" (it does not read 3925660 as listed everywhere on the web, so im assuming the zero was added later in production). So that gives me gear ratios of 2.52, 1.88, 1.47, 1.00 if my web-sleuthing skills are on par. I verified it has 10 spline input and 27 spine output shafts. If i go with this one then i have to get bellhousing and peripherals, i have no fork or clutch etc but my shed is a mess so those might still be hiding.
For the other transmissions, i have yet to find out if they will bolt directly to a bbc (i expect to find they probably do). They are also automatics, and i would be afraid of an ill-timed upshift causing a spin out (just ask my brother what happened to his 35th Anniversary TA Convertible, may it RIP!). So i'm leaning towards the muncie right now, and perhaps throwing a GV overdrive behind it for highway speeds.