Two blocks:
- one being freshened up that already has bushed lifter bores
- one for new build-up that retains OEM unbushed lifter bores

Two sets of IMM BB lifters:
- one low-use set of earlier style w/ taller lifter body
- one new set of current style w/ shorter lifter body

Assumption: The earlier style w/ the taller body would be better suited to the block that does NOT have bushed lifter bores because the taller body will be more stable in shorter unbushed bore.

Assumption valid?

NOTE: Picture showing different body styles is showing a damaged tall-body lifter from someone else's engine, not one that I'm using.

Brad,
Your assumption is valid, but I think the bigger issue is using the scalloped (for lack of a better description) lifter body in a stock lifter bore instead of a solid body style. There is a much better chance of catching an edge in the oil galley as the bores wear, along with a lot of oil flow running needlessly through the lifter area that would better serve staying down low. Think either lifter would be fine in a bushed block, and not to say you can't run them in a non-bushed block, but in a hi-lift cam situation, you need to make sure the lifter is not coming out so far as to expose the mid-section of the lifter.

Based on everything I'd researched ahead of any purchases, I'm not running big enough lobes to be concerned about the lifter body design causing oil control issues that you mentioned. FWIW, that was the same concern that I had, too.

The original intent of the post was about lifter body height. However, FWIW, I went w/ the IMM stuff because I wanted both oiling to the needle bearings (street use) and their .180" offset intake pushrod seats (using w/ Victor heads that require .600+" offset intake rockers).

Fair enuff.............

you didn't say what blocks are being used

Taller lifter makes the same diameter pushrod shorter = stiffer.
Example only: if the PR is 10" ball to ball, and the ends are 1/2" each, the tube is 9".
Running all the same parts in an 8-1/2" tube (9-1/2" OAL) is almost 19% stiffer.

Re: questions / comments above...

1. Both blocks are OEM 440 RB.

2. In this example, the pushrod length is the same w/ both styles of lifter; the taller body simply extends above the pushrod seat vs. being machined even with pushrod seat.