Have a 70's vintage Colt SP1, Would a heavy barrel flattop upper fit?  Am thinking a 20 or 22 inch barrel.  As far as upper brands what would be a good choice. And would the SP1 Colt bolt and carrier, charging handle fit on a new varmint upper. Any for Sale?  Thanks

I have a 20" Bushy V Match mounted on my Lg hole Blue label, There is an adapter pin you would need in order for it to work.
[url]http://www.bushmaster.com/shopping/lowers/nes-06.asp[/url]
If you are concerned, get a friend to loan you a newer small hole lower and try mounting it first.
If it fits, most likely any other Mil-Spec upper will.
As for using the same bolt/carrier, I would order the new upper with a dedicated unit, to avoid possible head space problems.

Gunslinger,  Thanks for the information, I measured the front pin and it is .315 so is the bigger pin diameter. This SP1 was made in 1977 according to the serial # list above on the message board. I will check out the link.