Think about it this way...Run a roller, forget it. Run a flat tappet and sure..it will make a few HP maybe 10 or so--and prevent lifter / cam wear problems but...the added cost could cover a rollers expense. Many of the old blocks we have available have lifter bores that are worn to the point that flat tappet success is a crapshoot--too loose on the lifter bore and you get trouble--throw a roller in and who cares--it will run great, no issues except maybe a little oil pressure loss but no big deal--no worse than needle bearing rockers etc. I only do it if I need to repair a valuable block. Run a roller and forget about the bushings. It cost alot because it is a big job and takes more time than you might imagine.