Minkman:
I'll try to answer some of your questions..
1)..as far as I know...the receivers are heat treated differently...so you can't use a high pressure cartridge like a 270 or 308 on a shotgun frame...
2)NEF doesn't sell any barrel blanks to fiddle around wit...but you can buy different barrels from NEF thru their barrel accessory program and have it fitted by them to the appropiate receiver...or you can purchase or trade different barrels with like mined individuals and fit them yourself on the appropiate frame...NEF won't warrenty any barrels not fitted by them...
3)I believe a 50-90 has been done here...and here's a picture of it...
4)I'm not sure about a 8 bore...but they do have a 10gauge shotgun...and the 12 gauge Ultra Slug Hunter is a 10 gauge barrel rifled out for a 12 gauge Sabot
5)I have no clue about a 32 gauge shot gun barrell or if they would fit...
Merry Christmas...and a Happy New year
Mac