A block without caps is nothing but a PITA and IMO not worth working on, since you cannot just get caps from another 400 and bolt them on- you have to get them milled down and have the main journals align bored/ honed to assure the main journal bore is perfectly straight (pricey machine work usually reserved for fitting 4-bolt caps to 2-bolt blocks).
Earlier blocks also only have 2 motor mount holes on the sides, and you need the later 5-hole block to mount it in a '71 Firebird. I personally would find a later 70-75 no.481988 400 block and start from there.
Geno
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