The RG-X won't blow you away in terms of power, it won't be all too different to the stock engine. If you must have pullstart, I think the Picco .26 would be your best bet for PS power. An 8port Race would be nice too, going along the lines of the above post.

You also don't need the Sports chassis to accept pullstart, most other bigblock PS motors use compact pullstart units which will fit fine with the standard kyosho engine mounts and all chassis units.

-uDi