Question: Does the HQ have it's original motor? If so in my view you must retain it. You can stroke it if you like (just keep away from Pro-Comp kits).
You have quite a few capable engine builders in the 'gong. Shane McDonald "Shanes Race Engines" is one.

I do question why you would want to throw money into stroking though. As you state it's a cruiser and 308 will motor a HQ around the streets quite well.

Seeing as genuine L31, M21 HQ Sandman's are rare as hens teeth. I'd be doing it as factory as possible. No way would I consider anything thing else. The value in that car is factory original.
Like I said you can stroke it if you really want a little more power (although not sure where you will need or use it) but retain it as factory as possible.

2 cents spent!