255 cam is a strong little cam for a 3.5hp motor and it will pull easy 7000+ rpm's in a flathead built right and it will pull hard if you don't watch it. I know only one person that ran a 255 in s 5hp block and that was david wulf. he had a big bore hs-50 with electronic ignition/hot coil ...etc...
great setup if you where looking go really fast. but maybe to much for a 3.5hp? I ran the same cam in my ohh motor on my thunderbolt. work great with a lot of gearing. last year I built a ohh motor for my drag bike and use that same cam with 1.3 rockers and that engine was awesome. pulled 8200rpm's at 125ft. just can't say enough how great that 255 cam can be in the right motor.
i too plan on building a side popper ,but it will have to wait till next fall. i have a newer style block that takes the billet rod. also has the roller bearing cover,steel sleeve. my plains where to just use a stock ohh steel cam with the compression release with a hot coil and maybe modify the cast flywheel little.
something to think about and you may know this from the pass from my postings. i tried to have tim weld up one of my ohh compression release cams and he could not do it. welding was not working good for him on that type of casting.
now ole4 had him weld one years ago and had no problems?
maybe dynocams might have better luck welding a comp-release cam and you can still get the 245 cam profile. just remember you have to weld in the area on the side cover where the cam bearing is. basically enclose it so the mechanical arm does not get damage and take the chance of damaging the whole engine.
depending on what you want to do and type of block you have? you can still go pretty damn fast with a stock steel ohh comp-release cam.
last time I talk to someone at dynocams about making a cam it was way over $100. I believe $150
not trying to rub it into you dave,but I do still have one more 245 cam. just the perfect cam for a hotrod Tecumseh flathead. ever if I had to pay dyno the $150 bucks.
it would be nice if they can weld up a ohh-cam...