My 63 Valiant came out with the 7.25 rearend it went out I slightly modified a 92 nissan picup rearend to go back in for the time being?
Anyway I found a monaco in the local junkyard with the 8.25 rearend will this swap into my valiant and if it will how much trouble am I heading into

You would need to do significant mods to make the Monaco rear work well in your Valiant. Spring perches would have to be cut off and new ones welded in place with narrower separation, and you'd need to address service brake, parking brake, and wheel bolt pattern issues.

What were these "slight" modifications you made to the '92 Nissan pickup rear axle?

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Too many people who were born on third base actually believe they've hit a triple.

is that a B body Monaco or a C body one 75-78 they actually made a B body version "monaco" and a "royal Monaco" C body. anything older called a monaco would definitely be a C.