Here you get an overview of all the layouts that are possible to build with a Heavymetal Keyboard. While most layouts can be achieved with the included Eon series PCB, there are some that require a third party PCB.

I linked the sources of alternative PCBs that I'm aware of. If you are aware of more compatible PCBs and sources, please let me know, so I can include them as well.

HMKB-40

The HMKB-40 is tiny and has an orthogonal layout.

hmkb-40-layout-eon40

40 Layouts

This is a very compact, orthogonal layout. Apart from the included Eon40 PCB, there are also other third party PCB options available for this.
Some like to use this as a macro pad. Thanks to QMK/VIA you can program the keys however you like.

HMKB-60

The HMKB-60 is available with many different plates that enable you to build all kinds of layouts, including some of the more exotic ones which squeeze an arrow cluster into the 60% layout.

hmkb-60-layout-plain60

60 STD Layouts

The "HMKB-60 STD/HHK/WKL" supports standard 60% layout and common ones like HHKB and WKL. Unified ANSI and ISO support. Available with the Plain-60 PCB but also as barebones kit without a PCB. Many other compatible 60% PCBs are widely available.

60 ANSI 61K Layout

The HMKB-60 is also available as barebones kit without a PCB. This way you can use one of the many standard 60% PCBs like the "DZ60RGB-ANSI V2". This has the standard 61 key ANSI layout and has hot swap sockets.

60 ANSI 63K Layout

HMKB-60 can be combined with this 63 key "DZ60RGB V2 HOT SWAP" PCB. This non-standard layout includes the arrow keys.

60 ANSI 64K Layout

The DZ64 is another PCB with a non-standard layout, including the arrow cluster. This has shifted 4th key row to get to 64 keys.

Available at KBDfans.

60 ISO 62K Layout

If you like the standard 60% ISO layout and prefer a hot swap PCB, the "CK60 ISO PCB" is an option for you.

This PCB is available at Candykeys.

60 ISO 64K Layout

I was surprised to find an 60% ISO layout PCB with arrow cluster. This one is basically the same layout as the DZ60-ANSI with 63 keys, just ISO.

This PCB is called "BM60 RGB ISO" and available here.

60 BW Layouts

Ortho users know this layout pretty well. This is possible with the "Boardwalk" PCB. HMKB-60 Boardwalk-A and -B can be combined with this PCB. A uses the standard 60% case, B uses the HHKB case.

HMKB-65

The HMKB-65 enclosure is available in three variants "Standard / One-blocker / Two-blockers". They can be combined with a few different plates. HMKB-65 is available as kit with Eon65 PCB. If you want to use the HMKB-65 with one of the many other compatible 65% PCBs, you can also get the enclosure as barebones kit without the PCB.

hmkb-65-layout-eon65

65 Std Layouts

Many 65% layouts are possible with the Eon65 PCB. Other 65% PCBs are compatible as well.

65 ANSI Layout

Many compatible 65% PCB do exist, most popular is probably the KBD67 series. The "KBD67 MARK II" has the standard 65% ANSI layout with 67 keys and has hot swap sockets.

Available for example at KBDfans.

65 ISO Layout

If you like the standard 65% ISO layout and prefer a hot swap PCB, the "KBD67 LITE RGB ISO HOT-SWAP" is an option for you.

This PCB is available at KBDFans.

HMKB-75

The HMKB-75 enclosure is available in two different variants. "FRC" means "full right column", "HRC" means "half right column".

hmkb-75-layout-eon75

75 Layouts

Here you see the possible layouts for the HMKB-75.

HMKB-80

The HMKB-80 enclosure is available in two different variants. Standard (STD) and Winkeyless (WKL). The HMKB-80 tries to be as close to the standard TKL as possible. Only non-standard detail is the function row, which is offset by only 0.25 units - this is usual for custom keyboards.

hmkb-80-layout-eon87

80 Layouts

Here you see the possible layouts for the HMKB-80. The KBD8X MARK II looks like it is compatible, not confirmed though.

HMKB-95

The HMKB-95 enclosure exists in only one variant. See the layouts...

hmkb-95-layout-eon95

95 Layouts

Here are the possible layouts. Classic and modern bottom row, ANSI and ISO, as expected. Nice, big plus key possible.