As a variation on this theme, I copied the existing ATmega328P entry in avrdude.conf, modified the id, desc, and signature to match the 328, and pasted it before the existing entry.
#------------------------------------------------------------
# ATmega328
#------------------------------------------------------------
part
id = "m328";
desc = "ATMEGA328";
has_debugwire = yes;
flash_instr = 0xB6, 0x01, 0x11;
eeprom_instr = 0xBD, 0xF2, 0xBD, 0xE1, 0xBB, 0xCF, 0xB4, 0x00,
0xBE, 0x01, 0xB6, 0x01, 0xBC, 0x00, 0xBB, 0xBF,
0x99, 0xF9, 0xBB, 0xAF;
stk500_devcode = 0x86;
# avr910_devcode = 0x;
signature = 0x1e 0x95 0x14;
pagel = 0xd7;
bs2 = 0xc2;
chip_erase_delay = 9000;
pgm_enable = "1 0 1 0 1 1 0 0 0 1 0 1 0 0 1 1",
"x x x x x x x x x x x x x x x x";
chip_erase = "1 0 1 0 1 1 0 0 1 0 0 x x x x x",
"x x x x x x x x x x x x x x x x";
timeout = 200;
stabdelay = 100;
cmdexedelay = 25;
synchloops = 32;
bytedelay = 0;
pollindex = 3;
pollvalue = 0x53;
predelay = 1;
postdelay = 1;
pollmethod = 1;
pp_controlstack =
0x0E, 0x1E, 0x0F, 0x1F, 0x2E, 0x3E, 0x2F, 0x3F,
0x4E, 0x5E, 0x4F, 0x5F, 0x6E, 0x7E, 0x6F, 0x7F,
0x66, 0x76, 0x67, 0x77, 0x6A, 0x7A, 0x6B, 0x7B,
0xBE, 0xFD, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00;
hventerstabdelay = 100;
progmodedelay = 0;
latchcycles = 5;
togglevtg = 1;
poweroffdelay = 15;
resetdelayms = 1;
resetdelayus = 0;
hvleavestabdelay = 15;
resetdelay = 15;
chiperasepulsewidth = 0;
chiperasepolltimeout = 10;
programfusepulsewidth = 0;
programfusepolltimeout = 5;
programlockpulsewidth = 0;
programlockpolltimeout = 5;
memory "eeprom"
paged = no;
page_size = 4;
size = 1024;
min_write_delay = 3600;
max_write_delay = 3600;
readback_p1 = 0xff;
readback_p2 = 0xff;
read = " 1 0 1 0 0 0 0 0",
" 0 0 0 x x x a9 a8",
" a7 a6 a5 a4 a3 a2 a1 a0",
" o o o o o o o o";
write = " 1 1 0 0 0 0 0 0",
" 0 0 0 x x x a9 a8",
" a7 a6 a5 a4 a3 a2 a1 a0",
" i i i i i i i i";
loadpage_lo = " 1 1 0 0 0 0 0 1",
" 0 0 0 0 0 0 0 0",
" 0 0 0 0 0 0 a1 a0",
" i i i i i i i i";
writepage = " 1 1 0 0 0 0 1 0",
" 0 0 x x x x a9 a8",
" a7 a6 a5 a4 a3 a2 0 0",
" x x x x x x x x";
mode = 0x41;
delay = 20;
blocksize = 4;
readsize = 256;
;
memory "flash"
paged = yes;
size = 32768;
page_size = 128;
num_pages = 256;
min_write_delay = 4500;
max_write_delay = 4500;
readback_p1 = 0xff;
readback_p2 = 0xff;
read_lo = " 0 0 1 0 0 0 0 0",
" 0 0 a13 a12 a11 a10 a9 a8",
" a7 a6 a5 a4 a3 a2 a1 a0",
" o o o o o o o o";
read_hi = " 0 0 1 0 1 0 0 0",
" 0 0 a13 a12 a11 a10 a9 a8",
" a7 a6 a5 a4 a3 a2 a1 a0",
" o o o o o o o o";
loadpage_lo = " 0 1 0 0 0 0 0 0",
" 0 0 0 x x x x x",
" x x a5 a4 a3 a2 a1 a0",
" i i i i i i i i";
loadpage_hi = " 0 1 0 0 1 0 0 0",
" 0 0 0 x x x x x",
" x x a5 a4 a3 a2 a1 a0",
" i i i i i i i i";
writepage = " 0 1 0 0 1 1 0 0",
" 0 0 a13 a12 a11 a10 a9 a8",
" a7 a6 x x x x x x",
" x x x x x x x x";
mode = 0x41;
delay = 6;
blocksize = 128;
readsize = 256;
;
memory "lfuse"
size = 1;
min_write_delay = 4500;
max_write_delay = 4500;
read = "0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0",
"x x x x x x x x o o o o o o o o";
write = "1 0 1 0 1 1 0 0 1 0 1 0 0 0 0 0",
"x x x x x x x x i i i i i i i i";
;
memory "hfuse"
size = 1;
min_write_delay = 4500;
max_write_delay = 4500;
read = "0 1 0 1 1 0 0 0 0 0 0 0 1 0 0 0",
"x x x x x x x x o o o o o o o o";
write = "1 0 1 0 1 1 0 0 1 0 1 0 1 0 0 0",
"x x x x x x x x i i i i i i i i";
;
memory "efuse"
size = 1;
min_write_delay = 4500;
max_write_delay = 4500;
read = "0 1 0 1 0 0 0 0 0 0 0 0 1 0 0 0",
"x x x x x x x x x x x x x o o o";
write = "1 0 1 0 1 1 0 0 1 0 1 0 0 1 0 0",
"x x x x x x x x x x x x x i i i";
;
memory "lock"
size = 1;
min_write_delay = 4500;
max_write_delay = 4500;
read = "0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0",
"x x x x x x x x x x o o o o o o";
write = "1 0 1 0 1 1 0 0 1 1 1 x x x x x",
"x x x x x x x x 1 1 i i i i i i";
;
memory "calibration"
size = 1;
read = "0 0 1 1 1 0 0 0 0 0 0 x x x x x",
"0 0 0 0 0 0 0 0 o o o o o o o o";
;
memory "signature"
size = 3;
read = "0 0 1 1 0 0 0 0 0 0 0 x x x x x",
"x x x x x x a1 a0 o o o o o o o o";
;
;
Also, added a new entry in boards.txt like so:
##############################################################
uno328.name=Arduino Uno w/ ATmega328 (non-P)
uno328.upload.protocol=arduino
uno328.upload.maximum_size=32256
uno328.upload.speed=115200
uno328.bootloader.low_fuses=0xff
uno328.bootloader.high_fuses=0xde
uno328.bootloader.extended_fuses=0x05
uno328.bootloader.path=optiboot
uno328.bootloader.file=optiboot_atmega328.hex
uno328.bootloader.unlock_bits=0x3F
uno328.bootloader.lock_bits=0x0F
uno328.build.mcu=atmega328
uno328.build.f_cpu=16000000L
uno328.build.core=arduino
uno328.build.variant=standard
This allows selecting my breadboard Uno-clone as a bootloader target. Trying to upload a sketch fails because the compiler doesn't have a matching target, but switching back to the proper Uno target works fine for that anyway. It's still easier than editing the conf file every time I swap chips.
I'm sure this can be made better, so if anyone wants to point out how... 