Hi!

First, I didn't do anything yet.
I have iMac late 2009 27'', Intel and two oprating system on: OS X Mountain Lion and FreeBSD. My partitions look like:
gpart show
34 1953525101 ada0 GPT (932G)
34 6 - free - (3.0K)
40 409600 1 efi (200M)
409640 1216587112 2 apple-hfs (580G)
1216996752 1269536 3 apple-boot (620M)
1218266288 1024 4 freebsd-boot (512K)
1218267312 727710720 5 freebsd-ufs (347G)
1945978032 7547102 6 freebsd-swap (3.6G)
1953525134 1 - free - (512B)

and gpart list:
Geom name: ada0
modified: false
state: OK
fwheads: 16
fwsectors: 63
last: 1953525134
first: 34
entries: 128
scheme: GPT
Providers:
1. Name: ada0p1
Mediasize: 209715200 (200M)
Sectorsize: 512
Stripesize: 0
Stripeoffset: 20480
Mode: r0w0e0
efimedia: HD(1,GPT,dbebc201-05d5-4cda-8a7a-72fb2f2e6c7f,0x28,0x64000)
rawuuid: dbebc201-05d5-4cda-8a7a-72fb2f2e6c7f
rawtype: c12a7328-f81f-11d2-ba4b-00a0c93ec93b
label: EFI System Partition
length: 209715200
offset: 20480
type: efi
index: 1
end: 409639
start: 40
2. Name: ada0p2
Mediasize: 622892601344 (580G)
Sectorsize: 512
Stripesize: 0
Stripeoffset: 209735680
Mode: r0w0e0
efimedia: HD(2,GPT,f0a96c0a-5ede-4b1f-b549-fcc134da186e,0x64028,0x4883a568)
rawuuid: f0a96c0a-5ede-4b1f-b549-fcc134da186e
rawtype: 48465300-0000-11aa-aa11-00306543ecac
label: Macintosh HD
length: 622892601344
offset: 209735680
type: apple-hfs
index: 2
end: 1216996751
start: 409640
3. Name: ada0p3
Mediasize: 650002432 (620M)
Sectorsize: 512
Stripesize: 0
Stripeoffset: 332079104
Mode: r0w0e0
efimedia: HD(3,GPT,eb095107-4503-47d6-9be0-e13881d01ea7,0x4889e590,0x135f20)
rawuuid: eb095107-4503-47d6-9be0-e13881d01ea7
rawtype: 426f6f74-0000-11aa-aa11-00306543ecac
label: Recovery HD
length: 650002432
offset: 623102337024
type: apple-boot
index: 3
end: 1218266287
start: 1216996752
4. Name: ada0p4
Mediasize: 524288 (512K)
Sectorsize: 512
Stripesize: 0
Stripeoffset: 982081536
Mode: r0w0e0
efimedia: HD(4,GPT,eb9589e7-2449-11e6-ac1d-0023dffff19f,0x489d44b0,0x400)
rawuuid: eb9589e7-2449-11e6-ac1d-0023dffff19f
rawtype: 83bd6b9d-7f41-11dc-be0b-001560b84f0f
label: (null)
length: 524288
offset: 623752339456
type: freebsd-boot
index: 4
end: 1218267311
start: 1218266288
5. Name: ada0p5
Mediasize: 372587888640 (347G)
Sectorsize: 512
Stripesize: 0
Stripeoffset: 982605824
Mode: r1w1e1
efimedia: HD(5,GPT,eb966422-2449-11e6-ac1d-0023dffff19f,0x489d48b0,0x2b5ffc00)
rawuuid: eb966422-2449-11e6-ac1d-0023dffff19f
rawtype: 516e7cb6-6ecf-11d6-8ff8-00022d09712b
label: (null)
length: 372587888640
offset: 623752863744
type: freebsd-ufs
index: 5
end: 1945978031
start: 1218267312
6. Name: ada0p6
Mediasize: 3864116224 (3.6G)
Sectorsize: 512
Stripesize: 0
Stripeoffset: 4203307008
Mode: r1w1e1
efimedia: HD(6,GPT,eb9c3676-2449-11e6-ac1d-0023dffff19f,0x73fd44b0,0x7328de)
rawuuid: eb9c3676-2449-11e6-ac1d-0023dffff19f
rawtype: 516e7cb5-6ecf-11d6-8ff8-00022d09712b
label: (null)
length: 3864116224
offset: 996340752384
type: freebsd-swap
index: 6
end: 1953525133
start: 1945978032
Consumers:
1. Name: ada0
Mediasize: 1000204886016 (932G)
Sectorsize: 512
Mode: r2w2e4

Now I have Seagate 1TB HD which is going down and I bought 500GB SSD drive. I will take the old HD out and install SSD drive. For me is OS X not important ecause I am usin 99.9% FreeBSD but on the disk should be partition 40 409600 1 efi (200M) that allow me to install just FreeBSD. I'll be very happy if I can also make and image of the HD but I am not sure because old and the new one have different size.

Thank you very much.