Still, you're approach is acceptable, and I find Example #2 preferable.
Let's use the Table & Example for advancement then.
Now that that's settled, shall start on the actual stats?
For a basic tombheart we'd better use two 11-HD Wardens as the linked Wardens, since that's the weakest it will go.
The current table says it'd be a Small Construct with 11 Hit Dice, although I'd be game for modifying the table to make them start out Medium-sized if you'd prefer them that way.
Its stats would probably be pretty similar to a Tomb Warden except for it being immobile and having 4 tendril attacks. The original version has tendrils that do 2d8 damage, but I'll assume that's for a Medium-sized Tombheart and scale the damage down for our Small basic 'heart.
So, we've got something like:
EDIT: Changed to start out Medium-sized and adding Dispelling Blow.
Golem, Tombheart
Medium Construct
Hit Dice: 11d10+30 (80 hp)
Initiative: +0
Speed: 0 ft. (immobile)
Armor Class: 16 (+6 natural), touch 10, flat-footed 16
Base Attack/Grapple: +8/+13
Attack: Tentacle +13 melee (1d10+5)
Full Attack: 4 tentacles +13 melee (1d10+5)
Space/Reach: 5 ft./5 ft.
Special Attacks: —
Special Qualities: Construct traits, damage reduction 10/bludgeoning, darkvision 60 ft., dispelling blow, fast healing 1, immunity to magic, low-light vision, wall bound
Saves: Fort +3, Ref +3, Will +3
Abilities: Str 21, Dex 11, Con —, Int —, Wis 11, Cha 1
Skills: —
Feats: —
Environment: Any
Organization: Buttress (1 plus 2-4 tomb wardens) or wall (1 plus 4-24 tomb wardens)
Challenge Rating: ?
Treasure: None
Alignment: Always neutral
Advancement: Special (see below)
Level Adjustment: —
Advancement
The size and Hit Dice of a Tombheart depends on the number, size and Hit Dice of the Tomb Wardens it is linked to. A Tombheart must be linked to at least two Tomb Wardens, which must all have the same Hit Dice. The Tombheart has a size and Hit Dice according to the following table:
'No. of Tomb'''''Tombheart
''Wardens'''''Size''''''Hit Dice
'''''2'''''As Warden''As Warden * 1
''''3-4''''As Warden''As Warden * 1.5
''''5-6''''As Warden''As Warden * 2
''''7-8''''Warden +1''As Warden * 2.5
''''9-12'''Warden +1''As Warden * 3
'''13-16'''Warden +2''As Warden * 3.5
'''17-24'''Warden +2''As Warden * 4
'''25-32'''Warden +3''As Warden * 4.5
'''33-40'''Warden +3''As Warden * 5
Example: A wall of seven Tomb Wardens will have a Tombheart one size larger than the Wardens with 2.5 times the Hit Dice of each Warden, thus the Tombheart of seven standard Tomb Wardens (Medium-sized 11 HD) is Large-sized and has 27 Hit Dice.
We'll need to modify
Wall Bound so it can only strike through stone with its tentacles and note that its Wardens can walk through it as easily as the rest of its wall.
Apart from that is their anything you'd like?
I wondered about Improved Grab and Constrict for the tentacles, but don't much like the idea - I prefer striking tentacles only.