I like it! Would be a unique, different project and bring out the best in both worlds.
The new PB seems to hit it right in a lot of areas and the price puts it over the top I think. All reviews I've seen have been good so far. Only drawback of that old frame is its weight, meaning it wouldn't be very mobile-one reason I parted with mine. I suppose if moving around was important you used pneumatic tires! LOL. A newer generation frame would take care of that-then again, I'm not sure how heavy the PB is. But whereas you already have the frame you're one step ahead.
I never thought I would enjoy pellets so much, after starting out with a Traeger that I didn't enjoy. But the Bullseye suits my cooking needs perfectly, hot and fast, and the Phoenix seems to follow suit.