PO used to sell the frames seperate and you could do as you stated. There is another company that makes a double stack frame but its name escapes me.
Ron

There are several companies that sell double stack .45 frames.  Caspian and Entreprise Arms are some other options to consider.

Be aware that ParaOrdnance uses a Series 80-style firing pin block so their frame will be cut for the extra parts.

I had a colt slide on my para and it worked just fine but you have to have a ramped barel for a para lower or was it I had a p14 upper on a tompson lower hell I don't rember but I do know it can be done. OK Im almost positive that you don't need a ramped barel after I think about it.p14 lower springfield upper yes It will work!!

You can use the product at the below link
to ditch the series 80 trigger parts.
All paras (except for F-series
gunsmith kits and then only as an option) will need a ramped barrel, as that is how the frames are cut.
I suppose you will have to find an
extended ramped barrel.

[url]http://www.brownells.com/Product/productDetail.asp?ProductID=010103100&CategoryID=0[/url]

Gunsmiths have many
different methods of fitting
frames to slides.