Newb with a 225 needs assistance

Small block will not fit on \6 K-frame without adaptive mounts.

You ought to be able to find a good used slant-6 for not much money. Use www.car-part.com . First search 1969 Valiant, then search 1980 Dodge Aspen, then search 1985 Dodge D150 truck. Three separate searches. All you'll have to do is use the oil pan and pickup pipe from a '67-up passenger car engine (such as your present engine) to adapt the truck engine.