Heartwood runics aren't typically used much for crafting or reforging.
For crafting (like any other tool) the mods & properties are too random. This is the same reason people don't use valorite hammers or barbed sewing kits for crafting anymore... in short you can get a better piece by reforging/imbuing.
For reforging if you were to use a heartwood runic you are basically going to get a couple deisred properties you will be able to select but since it is the highest runic you end up with additional properties you (of that same property type) that you don't wont. For the exact property details I suggest checking out UOGuide's write up on it found here (
Runic Re-Forging - UOGuide, the Ultima Online Encyclopedia) but an example would be that you want 40 SSI so you select "of haste" tag which could give you that property but since it's a heartwood it will give another 4-5 properties so you might also get +5 dex and +50 Stam leech and +9 Stam Regen (all things that take up spots for mods you want).
Basically what you want to do is use something like an ash runic kit that will allow for a "sweet spot" and reforging the "of haste" tag would potentially give you ONLY 40 SSI with no other properties since the runic level would allow that (it's not high enough to add more than 1 or 2 properties).
My suggestion is to use a GM exceptional bow to reforge with an ash kit using only "of haste" and shot for a 40% SSI bow. That will give you +40 DI & 40SSI and then you can take that bow and imbue 50% lightning and 15% HCI (although I'd suggest getting DI & HCI from your jewelry but that's up to you) and 1 more mod (maybe velocity). Once you have the bow imbued up to the max weight (make sure you use powder of fortification before you imbue!!) you can then use the forged artifact (for 100% chance enhancing) to enhance the bow with either Ash wood (to add +10 SSI for a total of 50% SSI) or Frostwood (adds +12 DI to bring you up to 52% DI).
Hope that helps.