Stock heads just need a little cleanup work and a decent valve job.
You can run a 4.3 S10 converter from the matching year S10 or Astro van in your 4L60E.
The long stroke of a 305 can tolerate a fairly decent cam before low-end torque is greatly reduced.
The L30 I setup had some roller lifters that were failing. I put a 218/218 @ 0.050 flat tappet cam into it and later ended up swapping Rhoads original lifters into it. I ran 1.6 full roller rockers. The Marine L30 used the 395' cam like the one used in the Ramjet/HT383. Made substantially more HP and TQ than a truck 305 Vortec. The marine L30 made 260 hp and ~310 TQ with s very similar overall torque curve. I had a Volant intake and long tube headers into dual 2.5" pipes and 2.5" thunderbolt high flow cats into a dual 2.5" in/single 3" out muffler on my Tahoe with the 305. I ported the stock lower intake. The S10 converter stalled about 2,500 rpm behind it. It had decent low-end torque even with 3.42 hears and 32" tall tires. The cam really came on above 3,000 rpm compared to the stock cam yet with the Rhoads lifters had just as much low-end as the stock cam and I set the WOT shift points to 5,500 rpm. At 70 mph it would loaf along at 1,750 rpm and I rarely found it kicking down to maintain speed. I pulled a 5,000 lbs trailer a few times with it. I would put the shifter in 3rd and go. It took a little RPM to get rolling from a stop but ran down the road really well at 2,500 rpm @ 70 in 3rd and would downshift to 2nd on hills but had no problem holding 70 mph uphill in 2nd gear at ~4,100 rpm.
