Your 98.5 will respond to the RV 275 injectors very nicely.
Since you are concerned with a margin of safety...the best combination you probably would benefit from would be the RV injectors and an EZ. Also, you can change the jumper pins in the EZ for different levels of performance. Therefore, I would test your towing and monitor your temps and boost with different settings on the EZ with the RV injectors.
Its a very nice combination and the ECM you have would only compliment it. Actually your ECM is probably close to what levels one and maybe 2 are on the EZ.

anyone else concur with this?

I would also address the exhaust and intake for towing.
I get lazy and do not read all of whats on a thread so maybe you did that already.



Good luck.

Did I mention the RV275's and EZ are a good combo?

 

*Bingo* "You get what you pay for." Here's a look at my pistons after running 5200 miles of 230HP injectors on my DAILY DRIVER. The spray pattern on the piston surface is all soot and was wiped off easily. There was zero scoring to the pistons themselves.

I actually prefer driving around and towing with the EZ connected. It's smoother and helps out on the low end torque.

 

I have the PM3 adj. it great for racing or towing. I tow around 29000# up 8% grades 6 miles on level 7 4th gear 2200 rpm at around 52-55 mph at 1250 +/- 50 degrees. If you stay at level 6 your clutch will be o.k. above that it will slip like crazy. I think the injectors would be nice for bottom end. Take off with the PM3 is the same as stock.