If you shop around you can get a good running G-62 for less than $300.00.
You won't need a pipe and they will last for ever.

I have one in a 108" Mr. Mulligan and it is impressive.

You can do a little research and come up with the weights.
I'll bet it's not that much more. And maybe even less if you go to full EI.

By the way the G-62 is a chainsaw engine and will turn 10,000rpm.

The only replacment fo cubic inches is cubic feet.