Have a 451 short block from joez. Hardblock,aluminum mains,aluminum rod, and B1 nitrous pistons. B1 originals with single 4 cast intake. Looking for cam spec recommendation.

What compression ratio will you end up with?
Who did the porting on the B1 original heads and/or what does the flow sheet look like?

best thing you can do is call Scott Brown, he can get you a good nitrous cam and he is familiar with this combination. Your heads will need chamber softening or your going to need some serious retard timing wise.

Tom Hemphill has a lot of both B1 and nitrous experience. He is located in Pa.

This sounds like a stock block build, is it? If so which block and year casting is it?
Did he (the engine builder) or you have the block sonic tested before starting?
I sincerely hope so, especially if it is a 400 block.
If it is a 440 block be very careful on how much power you make with it
IHThs

630 casting 400 block. Compression should end up around 11:1. No flow sheets yet on heads. Heads were down by Muscle Motors for a Top Dragster . Motor made a touch over 1000 with a 604. Softening chamber?

OVER 1000 with a stock block? be very careful with nitrous on it. Sounds a little optimistic to me, but im sure its possible just don't see how its going to live long that's all. IF you putting a healthy dose of nitrous on it, Single digit timing is where id start, but you didn't give any nitrous PPH numbers so im only speculating here.
Google Chamber Softening and im sure you will see whats involved. Basically it lays the chamber back and slows the flame front, allow more timing to be run or at least not be so timing sensitive for heads with small chambers like a B1

Assuming this is race-only?
The cam selection must include: how much nitrous?'

Chamber softening: convert all sharp edges into blended radius, dress down anything right at the spark plug, exhaust valve seat, and the dome's exhaust valve pocket.
If you have a chamber and/or piston photo, I may be able to identify obvious troublesome areas.

From what I have studied on the subject of chamber softening the general idea is to eliminate or relieve the quench pad and lay the chamber walls way back along with what was said above. It's something I want to try on the new combo here as well. Sure wish we could score an affordable cast iron low deck block! I have the same "630 casting" blues over here. Hopefully yours lived an easy life in a Cordoba or something because it's going to be hell from here on lol.

It is very easy to make over a 1000 HP N/A with a decent set of B1 with less than 450 C.I. with a tunnel ram and two good big carbs Those combinations like to make HP revved above 7000 up to 8600 RPM or so Think twice, build once
That combination won't live in a stock block though

I agree, the smallest error with nitrous (too soon, too much, too lean, too hot, too advanced) is fatal at that power level.

Heads came off a 604ci that made a touch over a 1000. Ill get some pics