What motor is it? A 4.3 is rated a 220, I have a older mercruiser branded 4.3 that is advertised at 235, its carbureted with a Rochester 2 v with hei ignition and
150 hp in a 1800 pound buggy will move ok. I thought you had a 4.3... Those are what we used to swap into stuff that a v8 wouldn't fit or wasn't wanted. I think those little v6's were rated for around 125 or so. Carb and ignition is about all I would do. If you wanted more, a different engine would be more money wise than upgrading it.
I'd love to go with a Buick 3.8 V6, but if I have to replace my GM 2.8 I'd go with either the 3.1 or 3.4 variation of the same motor. All the stuff I've invested in for the 2.8 would carry over.
My 2.8 started out at 135 hp with the MPFI...the carb variant was 125 hp...I'm hoping with my bolt ons to at least get back to 135, and I'll be happy if it made 150.