I've procured a few of the Jameco LM308N single opamps and they are indeed genuine. At least, they work in my Rat builds and sound the same when swapping between them and an OP07.
If you have one of those cheap Chinese GM-328 testers, you can use this diagram to verify a genuine 308 . . . .
And for the sake of simple pin-for-pin equivalents, here's a list of opamps that are swappable in their respective pin-outs . . . .
PIN-FOR-PIN Replacements with Slew Rates & Input Types. . . .
Single Op Amp Equivalents:
CA3130 - Slew = 10V/µs; MOSFET (In & Out)
CA3140 - Slew = 9V/µs; FET
LF351N - Slew = 13V/µs; FET
LF356 - Slew = 12V/µs; FET
LM201 - Slew = variable; BJT
LM301 - Slew = variable; BJT
LM308 - Slew = 0.3V/µs; BJT
LM148 - Slew = ~0.5V/µs;BJT
LM4250 - Slew = variable; BJT
LM709 - Slew = 0.25V/µs; BJT
LM741 - Slew = 0.5V/µs; BJT
LM748 - Slew = 0.5V/µs; BJT
MC1439 - Slew = ~6V/µs; BJT
MC33171N - Slew = 2.1V/µs; BJT
MCP601 - Slew = 2.3V/µs; MOSFET (In & Out; 6v MAX)
MCP603 - Slew = 2.3V/µs; FET
MUSES03 - Slew = 35V/µs; FET (very expensive)
NE5534 - Slew = 13V/µs; BJT
NJU7031 - Slew = 3.5V/μs; FET
OP07CP - Slew = 0.3V/µs; BJT
OPA134 - Slew = 20V/µs; FET
OPA602 - Slew = 20V/µs; FET
OPA1641 - Slew = 20V/µs; FET
TL061 - Slew = 3.5V/µs; FET
TL070 - Slew = 18V/µs; FET
TL071 - Slew = 13V/µs; FET
Dual Op Amp Equivalents:
AD712 - Slew = 16V/µs; FET
CA3240 - Slew = 9V/µs; FET
CA3260 - Slew = 10V/µs; FET
LF353 - Slew = 13V/µs; FET
LM248 - Slew = ~0.5V/µs;BJT
LM358 - Slew = 0.3V/µs (@ unity); BJT
LM1458 - Slew = 0.5V/µs; BJT
LM2903 - Slew = 1.3V/µs; Diff. Comparator; BJT
LM393 - Slew = 1.3V/µs; Diff. Comparator; BJT
LM4558 - Slew = 1.7V/µs, BJT
LM4559 - Slew = 2V/µs; BJT
LT1490 - Slew = 0.06V/µs; BJT
LM4562 - Slew = ~20V/µs; FET
uPC4570 - Slew = 7V/µs; BJT
LM4580 - Slew = 5V/µs; BJT
LM4562 - Slew = 20V/µs; FET
LM4582 - Slew = 20V/µs; FET
LM833 - Slew = 7V/µs; BJT
LMV652 - Slew = 3V/µs ~ 0.12 mA; BJT
MAE2741 - Slew = 1.6V/µs; BJT
MC33178 - Slew = 2V/µs; BJT
MCP6002 - Slew = ~0.6V/µs; MOSFET (In & Out; 7v MAX)
NE5532 - Slew = 9V/µs; BJT
NJM022 - Slew = 0.5V/µs; BJT
NJM4560 - Slew = 5.5V/µs; BJT
NJM4565 - Slew = 4V/µs; BJT
NJU7032 - Slew = 3.5V/μs; BJT
OPA1642 - Slew = 20V/µs; FET
OPA2107 - Slew > 9V/µs; FET
OPA2134 - Slew = 20V/µs; FET
OPA2604 - Slew = 25V/µs; FET
OP275 - Slew = 22V/µs; FET
RC4559 - Slew = 2V/µs; BJT
JRC2068 - Slew = 6V/µs; BJT
TL022 - Slew = 0.5V/µs ~ 0.13 mA; BJT
TL062 - Slew = 3.5V/µs; FET
TL072 - Slew = 13V/µs; FET
TL082 - Slew = 13V/µs; FET
TLE2072A - Slew = 38V/µs; FET
TLE2072C - Slew = 45V/µs; FET
Quad Op Amp Equivalents:
LF347 - Slew = 13V/µs; FET
LM324 - Slew = 0.5V/µs; BJT
LM348 - Slew = ~0.5V/µs;BJT
LM837 - Slew = 8V/µs; FET
LT1491 - Slew = 0.06V/µs; BJT
OPA1644 - Slew = ~20V/µs; FET
OPA4132 - Slew = ~20V/µs; FET
OPA4134 - Slew = ~20V/µs; FET
NJM4741 - Slew = ~1.6V/µs; BJT
NJU7034 - Slew = 3.5V/μs; BJT
TL074 - Slew = 13V/µs; FET
TL084 - Slew = 13V/µs; FET
TL064 - Slew = 3.5V/µs; FET
TLE2074A - Slew = 38V/µs; FET
TLE2074C - Slew = 45V/µs; FET