I downloaded and took a peek at your files. Noticed a few things after a cursory glance.
[BODY:SNOUT]
[BP:SNOUT:snout:STP][CONTYPE:HEAD][SMALL][CATEGORY:NOSE]
[DEFAULT_RELSIZE:20]
[BODY:SNOUT_NOSMELL]
[BP:SNOUT:snout:STP][CONTYPE:HEAD][SMALL][CATEGORY:NOSE]
[DEFAULT_RELSIZE:20]
Both of these have no smell. I'm assuming the smell token should be on the normal SNOUT.
[BODY:BASIC_HEAD_VBASE]
[BP:HD:head:STP][CON:NECK]CONNECTOR[HEAD][CATEGORY:HEAD]
[DEFAULT_RELSIZE:300]
Is the CONNECTOR intentionally bracketless? Note that it makes no sense here, either way.
Toady uses [CONNECTOR] on all necks that have [CONTYPE:HEAD], that way they keep the head on as long as they are still intact, even if the head basically gets destroyed itself. Thus, NECK has CONNECTOR (yours lacks this in the legacy parts, you should probably add it there) as it's a UB->HEAD->NECK construct and the neck acts (and is named) as upper spine for the head, while 7HEADNECKS does not have Connector, since the Hydra has a UB->NK1-NK7-> HD1-7 construct. In this case, the neck connects the head to the body automatically, and no CONNECTOR tag is required.
Also, MULTIHEAD8 to MULTIHEAD12 all connect to MULTINECK7, instead of the correct ones.
In the attacks file, for [CREATURE_VARIATION:ATTACK_PUNCH_BACKHAND_SLAP], both the slap and the backhand are named BACKHAND, I don't know if double-assigning the same attackname leads to conflicts or not, since I've never done that yet, just mentioning this.