EDIT(Apr 2013-current p/ns and added pic) Here are the current p/n for
12563532 flexplate to crank spacer $41.06 http://www.crateenginedepot.com/LS1-Fle ... 10346.aspx
19260102 flexplate $79.68 http://www.crateenginedepot.com/FLYWHEE ... 40667.aspx
19257940 bolts $5.28(need 6 bolts) http://www.crateenginedepot.com/LS1-Fle ... 10347.aspx
If you want to keep your 305 or 350 but have a more modern 4l60e/65e/70e that was behind a 4.8,5.3,6.0 or 6.2L engine then you need this kit.
$210.07
http://www.crateenginedepot.com/Transmi ... 10532.aspx
I find this interesting, because now I can install a 4l65e from a 2006 2wd SS Silverado into my 1997 2wd rcsb. The electronics are the same in all the 4l60e transmissions. The 4l70e has the TCM inside its case.
EDIT April 2013:
More p/n's for Auto Transmissions
AUTOMATIC TRANSMISSION
GMPP flexplate spacer 12563532 Scoggin-Dickey $40.81
GM flexplate for spacer 12551367 Scoggin-Dickey 113.00
GM metric flexplate bolts (6) 12553332 Scoggin-Dickey 2.52 ea.
GM LS1 Engine Kit Install Guide 88959384 Scoggin-Dickey 9.95
Hughes SFI flexplate, 168-tooth HP4004 Summit Racing 129.95
Hughes crankshaft adapter HP3795 Summit Racing 43.95
TCI Gen III/IV flexplate w/ext. 399753 Scoggin-Dickey 192.95
TCI Gen III/IV pilot extension 399753PE Summit Racing 29.69
And now for the Manual Transmissions:
MANUAL TRANSMISSION
Scoggin-Dickey clutch bracket SDCB Scoggin-Dickey $59.95
Keisler LS1 bellhousing call Keisler Engineering $239.95
Quick Time bellhousing 27011 Speedway Motors $374.99
McLeod flywheel 460535 Summit Racing $417.99
McLeod disc, 11-inch, 26-spline 260571 Summit Racing $225.99
McLeod pressure plate, 11-inch 360803 Summit Racing $194.99
McLeod clutch fork 16931 Summit Racing $60.69
McLeod adjustable ball stud 16908 Summit Racing $54.39
McLeod stock throwout bearing 16010 Summit Racing $63.69
McLeod adjustable throwout bearing 16505 Summit Racing $93.99
McLeod adapter pilot bushing 8617 Summit Racing $37.69
GM Gen III/IV flywheel 12561680 Scoggin-Dickey $299.60
GM metric pressure plate bolts (6) 12561465 Scoggin-Dickey $0.56 ea.
GM LS2/LS7 pilot bearing 12557583 Scoggin-Dickey $13.62
GM ball stud, short 3729000 Scoggin-Dickey $10.60
GM ball stud, long 3790556 Scoggin-Dickey $11.66
ARP metric flywheel bolts 330-2802 Summit Racing $26.95
ARP metric flexplate bolts 244-2901 Summit Racing $26.99
ARP metric pressure plate bolts 134-2201 Summit Racing $17.88
ARP metric bellhousing bolts 762-1004 Summit Racing $28.69
Throwout fork boot 178N Year One $11.30
Here are some torque specs that are needed. As well as crankshaft style(1 piece or 2 piece) and the bolt circle diameter
TORQUE SPECS
(ft-lb, unless specified)
Flywheel bolts
15 (1st pass)
37 (2nd pass)
74 (final pass)
Bellhousing bolts
37
Pressure plate bolts, ARP
35
BOLT CIRCLE DIAMETERS
CRANKSHAFT
REAR MAIN SEAL STYLE
BOLT CIRCLE (inches)
Gen I '55 to '86
two-piece
3.58"
Gen I '87 to current
one-piece
3.00"
Gen III/IV '97 to current
one-piece
3.11"
http://www.carcraft.com/techarticles/cc ... ewall.html
Edit April 2013: I added this pic as it shows the differnce in dimensions in the distance between the trans mount face and the very end of the crankshaft. The GEN 3 crank extends towards the trans furthur than a GEN 3 engine, so if you want a GEN 3/4 trans behind a GEN 1 engine, you need to space the trans back slightly with the GM kit 19154766. If you have a GEN 3 engine and want to use a trans that was from a GEN 1 vehicle, you will need the crank spacer 12563532, 6 longer bolts 19257940 and flexplate 19260102 .

I though some of you might find this interesting.
peace
Hog